David Cameron has hinted that Britain's withdrawal from Afghanistan could be speeded up amid speculation that the force size could be nearly halved next year.
In a video call, the Prime Minister and US President Barack Obama agreed that the plan for all combat troops to leave by the end of 2014 was "on track".
That meant there would be "further opportunities" for service personnel to be brought home over the next 12 months, according to the leaders.
Downing Street said Mr Cameron also discussed Syria, Iran and the Middle East Peace Process during the hour-long call.
"On Afghanistan, they discussed progress on the plan to hand security responsibility from the International Security Assistance Force (ISAF) to the Afghan National Security Forces, and agreed that the Nato strategy to withdraw combat troops from Afghanistan by the end of 2014 was on track," a spokeswoman said.
"This would present further opportunities for ISAF countries to bring troops home next year and they agreed to stay in close touch as detailed plans develop.
"They also agreed on joint work to strengthen the political process, particularly supporting Afghanistan and her neighbours to work together for stability, building on the trilateral discussions with Pakistan led by the UK."
Mr Cameron is widely expected to make a statement to MPs on Afghanistan on Wednesday - although Defence Secretary Philip Hammond is currently slated to deliver the update.
The UK contingent force is being reduced from 9,500 to 9,000 before Christmas. And there is speculation it could be cut to around 5,000 after next summer's fighting season.