Afghan President Hamid Karzai on Monday condemned the NATO mission in his country for causing "a lot of suffering" without delivering any gains.

The outgoing leader also suggested to the BBC that he might not sign a bilateral security deal wanted by United States.

"On the security front the entire NATO exercise was one that caused Afghanistan a lot of suffering, a lot of loss of life, and no gains because the country is not secure," he told Yalda Hakim of BBC World News.

"What we wanted was absolute security and a clear-cut war against terrorism."

Karzai revealed that he had "a very good relationship" with former US president George W. Bush until 2005, when civilian casualties began to mount.

Turning to the US security deal, which would detail the two countries' relationship beyond the planned NATO withdrawal in 2014, Karzai played down hopes of imminent agreement.

"If it doesn't suit us and if it doesn't suit them then, naturally we will go separate ways," he explained.

"If this agreement does not provide Afghanistan peace and security the Afghans will not want it."

The US hopes that a deal can be agreed before elections for Karzai's successor in six months time.

The president said the government was negotiating with the hardline Taliban, adding they will be welcome to participate in elections.

"Where it's the Afghan people appointing people through elections to state organs then the Taliban should come and participate in elections," said Karzai.

He insisted that the return of the Taliban "will not undermine progress" on women's rights.

Tens of thousands of civilians have been killed in Afghanistan since the Taliban launched their insurgency in 2001 after being ousted in a US-led invasion.

Violence has increased as NATO troops wind down operations and Afghan security forces take charge of security responsibility countrywide.

More than 1,000 civilians were killed and around 2,000 injured in the first half of 2013, according to a UN report, a 23 percent increase from the same period last year.

Peace efforts to contain the insurgency have so far failed to yield results.