NATO allies voiced hope Thursday that Afghan forces can take the lead across the country next year, with foreign troops in a backup role, as they seek to wind down a war that has dragged on for a decade.

At the same time, the alliance insisted that it was not changing plans to complete the security transition by the end of 2014 and that NATO troops would remain engaged in combat until then.

US Defence Secretary Leon Panetta had caused a stir before arriving in Brussels for talks with NATO counterparts when he suggested that Washington wanted to shift from a combat role to a "train and advise and assist role" by the end of 2013.

Panetta, seeking to clear up any confusion, told reporters after the first day of talks that NATO troops "will have to be fully combat-ready" and will fight "as necessary" even as Afghan forces assume the security lead.

"We hope that the Afghan security forces will be ready to take the combat lead in all of Afghanistan some time in 2013," the Pentagon chief said, adding that the final plan will be decided by NATO leaders at a Chicago summit in May.

The French defence minister, Gerard Longuet, was also compelled to clarify his country's position after President Nicolas Sarkozy announced last week that France would end its combat role by the end of 2013.

Longuet said French troops, numbering 3,600 today, would switch from a combat role to a training mission some time in 2013. France will gradually draw down troops and expects to leave around 400-500 military trainers after 2014.

"I was not criticised," Longuet told reporters. "Every country is thinking because each country is confronted with the same problems (in Afghanistan)."

Sarkozy's remarks had sparked concerns that a French withdrawal could encourage a rush to the exit, but a French official said Longuet told his counterparts that France was "committed to the Lisbon plan."

US President Barack Obama and French President Nicolas Sarkozy both face tough elections this year. War-weary voters could welcome a clear signal that US and French forces are nearer to leaving the unpopular war.

Despite NATO assurances that insurgents are on the back foot, a leaked secret NATO document, based on thousands of detainee interrogations, showed the Taliban believe they can reconquer Afghanistan once Western forces are gone.

Citing progress in the transition, NATO Secretary General Anders Fogh Rasmussen said was a "broad expectation" that Afghans can take over the lead in all provinces in 2013, but that it would depend on the "security and realities on the ground."

He insisted, however, that NATO was sticking to its 2014 calendar to withdraw combat troops from Afghanistan and that allies were committed to the principle of "in together, out together."

British Defence Secretary Philip Hammond said allies "all recognise that in 2013 there will be an evolution in the mission."

"The Afghans will be having lead responsibility for security throughout the whole country, but we will remain there in a combat support role and we will continue to do so in our case until the end of 2014," he added.

NATO has some 130,000 troops in Afghanistan, including 90,000 US troops.

By the end of September, the number of US troops is due to drop to 68,000, following the scheduled withdrawal of a "surge force" that deployed in 2010.

Panetta said no decision has been made on the level of US forces in 2013.