It will be up to Britain and other European states, and not the United States, to provide reinforcements for Afghanistan if it is decided more troops are needed, Nato sources said today.

Stanley McChrystal, the US general in charge of the overall Nato force of 100,000 has yet to make any formal request, and, according to a senior European official, he has been discouraged from doing so for the time being ‑ at least until there is a clear political settlement in the wake of Afghanistan's disputed election.

But if and when the call comes, the US will argue that it has already sent an extra 21,000 troops this year, and is still deeply committed in Iraq.

America already provides two-thirds of the Nato force. The pressure will instead fall on the European states.

"The Germans have more capacity, as do the French, the Italians and the United Kingdom," one Nato source said. The Americans would only be able to send in many more if they "draw down the numbers in Iraq", the source added.

But France, Italy and Germany would have thousands of troops available once peacekeeping missions in Lebanon and Kosovo were wound down, the source said. France has 2,000 troops in both the Unifil and Kfor missions, while Italy has around 2,500 in Unifil and 2,000 in Kfor.

The Nato official estimated that Britain's spare capacity was 2,000, and argued that British public support for continuing was surprisingly high in view of recent deaths of soldiers.

The pressure will increase if Canada carries out its intention to pull out its 2,800 troops from Kandahar province over the next 18 months. The future of Germany's 4,000 troops in northern Afghanistan will depend on the result of its general election later this month. Spain could commit a further 200 troops, adding to the 1,200 deployed there, Madrid said last week.

McChrystal has presented an strategic assessment to Washington and to Nato, and had been expected to supplement that report with a shopping list for more resources.

However, say European sources, the Obama administration was unhappy to see reports quoting the commander discussing the need for thousands more soldiers before all the 21,000 ordered in by Obama had even arrived ‑ 6,000 have yet to deploy in the country ‑ and McChrystal was told to suspend any formal request for more troops. "They have to bear Congress in mind. This needs to be a time to calm things down, and not to talk about sending more troops. Let us wait and see what comes out of the [Afghan] election," a European diplomat said.

Few if any western governments still expected a strong unitary and democratic state to be created in Afghanistan, particularly in the wake of the presidential election, the result of which is still being wrangled over in Kabul.

"No one ever thought this was going to be a free and fair election," a Nato official said.

Instead, western governments now envisaged "a decentralised, tribal society, large parts of which will be run by people we may not like but who will not allow al-Qaida to train and to plot to kill Americans or Germans or Brits".Nato officials insisted today that the alliance's cohesion was holding in the face of a worsening insurgency and rising casualty rates. They pointed to the reduced number of "caveats" - national restrictions on what the kind of operations some troop contingents can take part in.