The UN Security Council on Wednesday demanded immediate and "unhindered" access to hundreds of thousands of civilians trapped in the Syrian conflict.
A statement drawn up by Australia and Luxembourg, which includes a call for cross-border humanitarian operations, is the council's second major united decision on the war in less than a week.
The council had been deadlocked since the start of the 30-month-old uprising against President Bashar al-Assad until it passed a resolution last Friday ordering the destruction of Syria's chemical weapons.
Russia has defended Assad at the Security Council but backed the chemical weapons resolution and Wednesday's statement, which does not have a legally binding status.
Council diplomats said the statement would send a strong signal to the Assad government as the death toll of more than 100,000 and the humanitarian crisis grow.
UN aid agencies say there are more than 2.1 million refugees outside the country, almost six million have fled their homes inside the country and they have not had access to about two million trapped civilians for several months.
The council statement urged both sides but "in particular the Syrian authorities" to help UN agencies and private aid groups "to provide immediate humanitarian assistance to the affected people in Syria."
It called on Assad's government "to take immediate steps to facilitate the expansion of humanitarian relief operations, and lift bureaucratic impediments and other obstacles."
Aid agencies say the government has held up visas and restricted the number of foreign groups allowed to operate in Syria.
The statement says there should be "unhindered humanitarian access" across the conflict lines "and, where appropriate, across borders from neighboring countries."
The Syrian government has opposed aid missions from neighboring countries, saying the supplies will go to rebel forces. Some analysts have expressed doubt that rebel groups will let aid go to government areas.
Australia's UN ambassador Gary Quinlan said the statement was "a strong unified" message from the council that humanitarian work must not be impeded.
He said there had been a "need for speed" in agreeing on a statement rather than a binding resolution because of the "terrifying" events in Syria.
UN humanitarian chief Valerie Amos has been pressing the Security Council for several months to act on the growing crisis.
Amos said after the statement was agreed that it meant more effective work could be done but that humanitarian workers in Syria have to be "protected."
"Our task now is to turn these strong words into meaningful action," Amos told reporters.
"If the commitments and practical steps in this statement are implemented, humanitarian workers will be able to reach over two million people who have been unreachable for many months," Amos told reporters.
The UN has predicted that the number of refugees in countries around Syria will increase to three million by the end of the year. Amos said aid efforts will have to be stepped up before winter arrives.
UN agencies have an estimated $3 billion funding shortfall for their Syria relief efforts, and UN leader Ban Ki-moon is to hold a new conference to rally financial support in Kuwait in January, diplomats said.
Syria's UN ambassador Bashar Jaafari welcomed the statement but said it would be up to the Damascus government now to decide how to help the UN.
Aid and rights groups quickly welcomed the statement.
"If the Assad government continues to drown humanitarian agencies in red tape, including by refusing cross-border aid from neighboring countries, it will be a direct challenge to the Security Council’s authority," said Philippe Bolopion, UN specialist for Human Rights Watch.
However some doubts have been raised over how far the statement will be applied. The opposition Syrian National Coalition also welcomed the statement without saying how far it would cooperate.
"It may create more headaches for the rebels than for Assad. Will rebels let aid into government-held areas?" said Richard Gowan, a director of New York University's Center on International Cooperation.