Head of the British army General Peter Wall cast doubt on Prime Minister Cameron's 2015 deadline for the withdrawal of combat troops during an interview for a BBC documentary due to be aired Wednesday.

"Whether or not it turns out to be an absolute timeline or more conditions-based approach nearer the time, we shall find out," Chief of the General Staff Wall told the "Afghanistan: War Without End?" programme.

Meanwhile, former army chief Richard Dannatt urged Cameron not to be tempted to accelerate the withdrawal by US President Barack Obama's expected announcement that 10,000 US soldiers are to be brought home.

"Obama may wish to withdraw troops for his domestic political purposes but I am quite sure our prime minister will not fall into the same trap," the former soldier told The Times.

"He will not want to risk the investment in blood and treasure just for a domestic political agenda," he added.

Cameron reacted testily on Tuesday to an air force chief's claims that fighting in Afghanistan and Libya was demoralising personnel, saying Britain could continue its Libya operations for "as long as is necessary".

In a leaked briefing paper, Air Chief Marshal Simon Bryant, the deputy head of the Royal Air Force (RAF), warned its ability to carry out future missions would be under threat if Britain's involvement in Libya extended past the summer.

Last week First Sea Lord Admiral Mark Stanhope, the head of the Royal Navy, also warned that the armed forces, slimmed down by budget cuts, would have to make tough choices if the Libyan campaign lasts more than six months.

At a press conference Tuesday, Cameron showed his impatience with the remarks, saying: "There are moments where I wake up and read the newspapers and think, 'Look, tell you what, you do the fighting and I'll do the talking.'"

But he said he had spoken to the head of the army and the first sea lord, and "they are absolutely clear that we are able to keep up this mission for as long as is necessary, and that time is on our side, not on (Moamer) Kadhafi's side".

Cameron said "the pressure is turning up all the time" on the Libyan leader, citing desertions from the regime and continued pockets of resistance in the west of the country, where Kadhafi's forces remain in control.

Copyright APP (Associated Press of Pakistan), 2011

Copyright AFP (Agence France-Presse), 2011