British General John McColl had talks in Kabul
The first elements of the force - about 200 British troops - will arrive in the Afghan capital, Kabul, by Saturday, Britain's Ministry of Defence has confirmed.
The 16 countries which have offered to contribute troops are to hold further talks in London on Wednesday about the force's make-up.
But differences remain unresolved on the overall number of troops to be sent.
Initial reports that the Afghan interim government might accept 5,000 troops have been denied by a spokesman for Defence Minister Mohammad Fahim.
General Fahim is known to want a smaller force and insisted that negotiations were still continuing.
British and American officials are to discuss the links between the international force and US troops already in Afghanistan.
Disagreements between Britain and Germany on the issue appear to have been resolved.
The numbers game
Some leaders of Afghanistan's anti-Taleban Northern Alliance, who are to hold senior posts in the new government, want to restrict foreign forces to a minimum.
The Afghan defence minister said last week that he saw no need for more than 1,000 foreign soldiers to be based in Afghanistan.
But the United States and Britain say a force of 3,000 to 5,000 troops is needed to maintain security.
The BBC's Daniel Sandford, reporting from Kabul, says the strength of the force is a highly sensitive issue in Afghanistan.
It is not to be a formal United Nations peacekeeping force, but would be designed to provide stability in a country where war has become a way of life.
The British soldier expected to lead the international force, Major General John McColl, is returning home after two days of talks with the incoming administration in Kabul.
Europe disagrees
Britain says it will commit up to 1,500 British troops for several months.
The first contingent is expected to arrive in Kabul by Saturday, before the new administration is sworn in.
The 200 members of 40 Commando will be drawn from troops already securing the Bagram airbase outside Kabul and from those currently on board the assault ship HMS Fearless.
France has become the latest country to pledge troops for the force. It says up to 800 could be made available. Spain is to provide 700.
Exact details on the composition of the force are to be finalised in London on Wednesday during a meeting of military representatives from the contributor nations.
Britain and Germany had disagreements over relations between the international force and US troops in Afghanistan.
Germany is pressing for separate command and control structures for the two contingents. But Britain has called for close ties with the Americans.
Although this appears to have been overcome, Germany also remains unhappy with Britain's offer to lead the force for the first three months and then scale down its presence in Afghanistan.
Berlin is arguing that British troops should stay in Afghanistan throughout the mandate of the interim administration.