British troops will be in Afghanistan to start peacekeeping preparations by the weekend, the defence secretary said on Tuesday.

Geoff Hoon said that British troops heading the peacekeeping mission would not overstretch UK forces.

He said the mission would be "time limited" and "would last a small number of months".

Hoon's comments followed the announcement by Tony Blair that Britain is "willing in principle" to lead the Afghan stabilisation force.

Speaking in the House of Commons on Monday, Blair confirmed that troops were to begin arriving in Afghanistan later this week - saying that the total deployment will be no more than 1500 troops.

Whilst stressing that the final format of the proposed force is still under discussion, the prime minister signalled that the first troops will arrive on the ground within days.

"There remains unanimous support for the military action which has been taken in Afghanistan and a determination to continue our efforts to root out the Al Qaeda network," he said.

He said that December 22 - the date when the new interim government takes control in Afghanistan - was an "important date" but rejected claims that the full quota of British troops will be on the ground by then.

"This force was a critical part of the agreement reached in Bonn on December 5 for the establishment of a provisional government," he told the Commons. "We know that is only the start of enabling Afghanistan to cease being a failed state and become a responsible partner in the region."

Whilst he reconfirmed Britain's commitment to lead the stabilisation operation, ministers are stressing that more work still needs to be done before the full deployment can be given the go ahead.

The force will comprise of troops from the EU as well as Argentina, Australia, Canada, the Czech Republic, Jordan, Malaysia, New Zealand and Turkey.

The UN security council is expected to pass the necessary resolution next week and the US has given its full support, the prime minister said.

For the Conservatives, Iain Duncan Smith said he had "deep misgivings about the whole British deployment in such a mission".

There were elements within Afghanistan that were unhappy with the settlement agreed in Bonn and there were still Taliban units that would target British forces, he warned.

Drawing on his military experience he called on the government to ensure British units were given full back-up and the right equipment.