Syria, rocked by an armed revolt against president Bashar al-Assad since March 2011, has retained close links with Russia, an ally since Soviet times from which it buys most of its weaponry.

Russia has maintained military sales to Syria throughout the two-and-a-half-year conflict in which over 100,000 people have been killed, and helped block three United Nations draft resolutions criticising Mr Assad's crackdown on the mainly peaceful protests against him in 2011.

More recently, Russia has backed Mr Assad's claims that the rebels were responsible for an alleged chemical attack which is believed to have killed up to 1,400 people on August 21.

Their view contradicts that held by the United States, United Kingdom and France, who have led the way in saying that Mr Assad ordered the attack.

Russia is also against proposed military strikes on Syria which US president Barack Obama has suggested he would be prepared to carry out without the authorisation of the UN.

While the US has the backing of France and the UK, Mr Putin has used the G20 summit to garner support from nations opposing military action - at least until the UN investigators have released the findings of a recent mission to the sites of alleged chemical attacks.

So far representatives from China, the EU and Germany have spoken against unilateral military strikes.

Like Mr Assad, Mr Putin has warned the US and its allies against using force saying that without UN approval, it would be seen as an aggression.

Mr Putin said Russia did not rule out supporting a UN Security Council resolution authorising force, if it was proved "beyond doubt" that the Syrian government had used chemical weapons.

Whether the basis for Russia's backing of Mr Assad stems from an economic or ideological stand point, take a look back over the country's involvement in the Syrian conflict, what Mr Putin has said and what possible motivations are behind the support.

Russia and China block a declaration submitted by Western countries at the UN condemning repression of peaceful protests by Mr Assad's government.

Russia's then president Dmitry Medvedev tells Mr Assad either to reform or resign, while warning the West that Russia will fight outside attempts to oust him.

A large Russian flotilla led by an aircraft carrier docks at Tartus, a port where Moscow leases a naval base from Damascus. In April, a top defence official tells the Ria Novosti news agency Russia will keep a permanent presence on the Syrian coast.

Mr Putin says Russia is concerned about the "growing threat" of an attack on Iran over its nuclear program, warning that the consequences would be "truly catastrophic".

MrPutin says his country doesn't support any side in the Syrian conflict and hasn't supplied arms that could be used in a civil war.

US president Barack Obama and Mr Putin call for an immediate end to the conflict in Syria after meeting on the sidelines of the G20 summit in Mexico.

World powers meeting in Geneva agree to a plan for a transition in Syria, before differences emerge over its interpretation.

Russia and China veto for a third time in nine months a Western-proposed UN Security Council resolution that would threaten sanctions against Assad if he does not end the use of heavy weapons.

The Russians were still unhappy with the Arab plan for a political transition.

Ankara forces a Syrian passenger plane from Moscow to Damascus, reportedly carrying arms, to land in the Turkish capital

Russia only has a "working relationship" with Mr Assad, Medvedev - now prime minister - says, insisting that "privileged" ties were a thing of the past.

In a rare attack on its ally, Russia accuses Mr Assad of having made a "grave, perhaps fatal error" by delaying political reforms.

Russian foreign minister Sergei Lavrov warns that any move to arm Syrian opposition forces would contravene international laws.

: Russia calls Syrian opposition claims of the Damascus regime launching a chemical weapons attack that killed more than 1,300 people a "premeditated provocation".

Russia's foreign ministry warns a military intervention in Syria could have "catastrophic consequences" for the region. A Russian deputy prime minister says Western countries are behaving in the Islamic world like a "monkey with a grenade".

It emerges that Russia has sent a reconnaissance vessel from its Black Sea fleet to the coast off Syria.

Mr Putin suggests Russia could approve military strikes against the Syrian regime if the West presents watertight evidence of chemical weapons crimes but warns the use of force without UN approval would be an "aggression".

He reveals that Russia has suspended deliveries of sophisticated S-300 missile systems to Syria.

Mr Putin warns the US against any military action in Syria without UN approval.

Historically, Syria and Russia enjoy a stable and strong relationship. Syria helped the Soviet Navy out during the Cold War in 1971 by leasing them the Port of Tartus.

That same year, Hafez al-Assad - the current Syrian president's father - made his first visit to a foreign country after his accession to power by travelling to Moscow in February 1971.

The USSR and Syria had already established a military and economic relationship 15 years prior to the visit, but Hafez Assad demanded more military and economic aid.

In 1980, the two countries signed the Treaty of Amity and Cooperation which stated "the parties shall promptly contact each other incase the peace and security of one of the parties has been threatened for the purpose of eliminating that threat and re-establish the peace."

The relationship took a back seat under the leadership of Mikhail Gorbachev, the USSR established relations with other Middle East countries - particularly Israel - and as a result, the nation's focus switched from finding allies to creating new economic opportunities.

After the collapse of the Soviets and Boris Yeltsin’s accession to power, the newly born Russian nation no longer provided economic and military aid - though their presence at Tartus continued.

It was not until Mr Putin and Mr Assad came into power that Russia and Syria's relationship was revived.

Russia has a huge commercial interest in Syria.

Contracts it has signed with the country are reported to total a value of $5 billion and, bearing in mind what happened with Iran, (Russia lost an estimated $13 billion due to international sanctions), Mr Putin and his government will be eager to protect their deals.

Russia is also believed to have lost $4.5 billion in negated contracts with Libya, so the arms industry has taken enormous hits in recent years.

Professor Daniel Triesman of the UCLA Department of Political Science also suggests that a number of Russian companies have investments in Syria's infrastructure, energy and tourism sectors which in 2009 had a total estimated value of $19.4 billion.

In a bid to change Russia's stance, Saudi Arabia last month offered them economic incentives including a major arms deal and a pledge not to challenge their gas sales if Moscow scaled back support for Mr Assad.

The proposed deal between two of the leading power brokers in Syria's devastating civil war was set out by Saudi intelligence chief Prince Bandar bin Sultan at a meeting with Putin in Moscow.

Syrian opposition sources close to Saudi Arabia said Prince Bandar offered to buy up to $15 billion of Russian weapons as well as ensuring that Gulf gas would not threaten Russia's position as a main gas supplier to Europe.

In return, Saudi Arabia wanted Moscow to ease its strong support of Mr Assad and agree not to block any future Security Council Resolution

If Russia turn against Syria it would also lose its leased naval facility in the port of Tartus - which gives the country its only access to the Mediterranean.

The facility was created during the Cold War and served to support the Soviet Navy fleet.

Since the collapse, Russia has retained a presence at the port and reports suggest it has plans to expand.

As of May 2013, Russia has sent a dozen or more warships to patrol waters near Tartus.

Many experts carry the belief that Russia's goal is often to undermine Western international objectives - mainly America's with Mr Putin very critical towards US involvement in Kosovo, Afghanistan, Iraq and Libya.

Russia's government is generally viewed as being somewhat conservative - it does not support revolution. It does not believe that wars and bids to over throw governments can lead to democracy and often refers to the US invasion of Iraq to make this point.

In 2011, Russia abstained from the UN Security Council vote authorising the a no-fly zone in Libya. This subsequently meant the bill was passed but given the flow of violence which ensued, Russia argued that NATO had gone beyond the mandate to protect civilians.

Russia points out that life post Muammar al-Gaddafi in Libya is chaotic and it fears something similar will happen in Syria. It also fears that Syria would be worse still with regard to sectarian violence.

Shi'ite Iran is Syria's closest ally and has accused an alliance of militant Sunni Islamists, Israel and Western powers of trying to use the conflict to take over the region.

As well as backing Assad, Iran also supports the Lebanese Shi'ite militant group Hezbollah which has sent fighters into Syria to help the government there.

"We want to strongly warn against any military attack in Syria. There will definitely be perilous consequences for the region," Iranian Foreign Ministry spokesman Abbas Araqchi said last month.

There's also the fact that a US strike on Syria could scuttle Iranian president Hassan Rouhani's big plan to fix Iran's economy by winning some relief from Western sanctions

Mr Rouhani's June election landslide won him the cautious backing of Supreme Leader Ayatollah Ali Khamenei to pursue his pledge to engage with Western countries and attempt to ease Iran's isolation over Tehran's nuclear program.

"The atmosphere between Syria's allies and the West, after a Western attack on Syria, will become so cold and dark that there would be practically no space for reducing tensions and improving relations. Iran will be forced to change its tone towards the West to a hostile one," wrote Sadeq Zibakalam, a professor at Tehran University.

Foreign minister Mohammad Javad Zarif went further, blaming Syrian rebels. He also warned the United States not to get involved: "The Syria crisis is a trap set by Zionist pressure groups for (the United States)," Iran's English-language channel Press TV quoted him as saying.

More recently, Iran's military chief has said the country will "support Syria until the end."

Iran has also accused the US of using its claims that Syria's forces had unleashed chemical weapons on civilians last month as a "pretext" to try to topple Mr Assad's regime.

China and Syria have close trade links (it was Syria's third largest importer in 2010 according to reports) but it does not seel them weapons nor does it rely on them as an ally.

Among the theories about its support for Syria is the fact that as a nation, China is so against foreign involvement and has never supported the use of force against a regime nor has it encouraged or backed foreign intervention.

There is also the matter or Libya. China, like Russia, vetoed the UN resolution in 2011.

Again, like Russia, China believes that the action against Libya went beyond the mandate and they do not want to see a repeat of the chaos in Syria.

"A political solution is always the only realistic means to resolve the Syria issue," Chinese foreign minister Wang Yi said recently.

This was followed by Chinese delegation spokesman Qin Gang saying "war cannot solve the problem in Syria" at the G20 summit.

China has also expressed concern about what effect military action would have on the economy and the price of oil.