Foreign Secretary David Miliband today renewed his call for other countries to put more troops into Afghanistan, as he arrived in the country to visit British forces.
He did not rule out an expansion of the UK's military presence although reports that an extra 2,000 were to be sent were "invented", he told BBC Radio 4's Today.
US president-elect Barack Obama is expected to call for a troop "surge" when he takes office next year but British ministers want allies to bear a greater burden.
"We want to make sure we are playing our full role. But equally we've got to make sure that all countries are bearing their fair share of the burden. That's the discussion we will have," he said.
"The Germans have increased their number of troops, ditto the French, but we want to make sure there is a clear strategy, that it balances the economic, political and security and that it requires a fair effort from the whole of the international coalition."
The Foreign Secretary said he would tell Mr Obama: "Any question of more troops depends on what they would do and whether they were part of a genuinely comprehensive strategy.
"The most important thing to say is that the biggest source of new troops for the medium term is the Afghan national army, which I will be visiting later today."
Asked about suggestions 2,000 more British soldiers could be sent in, he said: "It is certainly invented as far as I'm concerned. I haven't seen any papers come to me saying we need 2,000 more troops."
"The MoD organises these assessments of what's needed in a very coherent, very systematic way and we are not going to do it on the basis of plucking numbers out of the air."
Mr Miliband said any civilian casualties were "a real blow".
"When innocent civilians are killed, their brothers and sisters and neighbours ask: 'what are you here for?' The critical thing is that we hold our hands up when things go wrong and that we insist that the vast bulk of the security work being done by British and coalition troops is to protect this country not to attack it."
The Foreign Secretary's visits comes the day after a Royal Marine was killed in a blast.
The death took the number of British service personnel killed in Afghanistan since the start of operations in October 2001 to 126.
Mr Miliband will visit troops in Helmand province and speak with military and political leaders before moving on to Pakistan tomorrow for talks with president Asif Ali Zardari.
He said they would discuss, among other things, ways for Pakistan to work "in the closest way possible with the American authorities" following controversy over US air strikes on its territory near the Afghan border.