PM backs small Afghan withdrawl

However, he added the withdrawal would be quite small and not affect the core force over the next year.

Highlighting the fragility of security gains in the near decade-long conflict, his trip to the town of Lashkar Gah in Helmand province had to be cancelled so that resources could be concentrated on finding a soldier who went missing yesterday.

"The campaign is moving into a new phase. You do see an increasingly confident Afghan national army and Afghan police able to carry out more operations on their own," he said, speaking at Camp Bastion in southern Helmand province.

"We are looking at a proper transition taking place, including the town of Lashkar Gah itself and, as that happens there will be opportunities to bring some British soldiers home, but we're talking relatively small numbers."

Mr Cameron insisted that the withdrawal would not affect Britain's core force for the next season of fighting - which runs from spring through to early autumn in Afghanistan.

He was speaking during an unannounced trip to Helmand, one of Afghanistan's most violent regions, where most of the 9,500 British troops are based. Mr Cameron said he had cancelled his trip to Lashkar Gah, where British and other Nato-led troops expect to start handing power over to Afghan forces on 20 July.

The Prime Minister is expected to detail the troop withdrawal in parliament tomorrow. It is thought he will announce a drawdown of between 500 and 800 troops by 2013.

Last month, US President Barack Obama, under pressure to start to draw an increasingly unpopular war to a close, announced the withdrawal of 10,000 US troops this year and 23,000 by September 2012.

Analysts say risk factors may become more acute under Mr Obama's exit plan, and some US military chiefs have voiced their discomfort over the speed of the withdrawal. Britain aims to withdraw all of its troops by the end of 2014.