Nato was last night trying to head off a full-blown crisis of credibility as allied defence chiefs failed to offer any extra troops to help hard-pressed soldiers fighting Taliban insurgents in Afghanistan.

With commanders on the ground urgently demanding reinforcements, Britain and the US raised the stakes in the struggle to get their Nato partners to provide more forces to defeat the Taliban in what they described as the biggest test facing the alliance in its 57-year history.

"No formal offers were made at the table," Nato spokesman James Appathurai said after a meeting of national defence chiefs at allied military headquarters in Mons, Belgium. But he said there were "positive indications" from some allies that they might consider providing extra forces to help British, Dutch and Canadian troops fighting Taliban fighters and their supporters in fierce, daily clashes.

He did not elaborate. However, defence sources told the Guardian that Germany, Poland and Norway might be persuaded to contribute to a 1,000-strong reserve battalion. Although significantly less than the 2,500 asked for last week by Nato's top commander, US General James Jones, it is the main priority of Lieutenant General David Richards, Nato's commander in Afghanistan, who has been asking for a reserve battalion for more than a year.

Commanders in southern Afghanistan say 1,000 extra soldiers could provide better protection for British and Canadian troops caught in isolated positions and help defeat Taliban forces more quickly and more convincingly.

The British defence secretary, Des Browne, is engaged in a private round of talks with his Nato counterparts and the organisation's secretary-general, Jaap de Hoop Scheffer, in the increasingly urgent search for an agreement. "There are still avenues to pursue," a source close to Mr Browne said last night. Whitehall sources said Britain, with more than 4,000 soldiers in southern Afghanistan and more than 7,000 in southern Iraq, was not in a position to provide any more.

Ambassadors from Nato countries will meet informally on Friday to help pave the way for a meeting of allied foreign ministers in the margins of the UN general assembly in New York next week.

Mr Appathurai said yesterday that it could take until Nato defence ministers met on September 28 in Slovenia before offers of extra troops are finally agreed and that deployment could have to wait until October. That is close to the onset of severe weather, which could curtail Nato operations in the south of the country.

Despite a shortage of troops, Mr Appathurai said Operation Medusa - the recent offensive against the Taliban - was "going well". "It is not complete yet, but I can tell you that a significant proportion of the objective has now been taken, in fact over two-thirds of the objective has now been taken."

Tony Blair said yesterday that it was "of fundamental importance to the security of this country, never mind the world, that we make sure the job in Afghanistan is done properly". After talks with the Chinese prime minister, Wen Jiabao, he told reporters at Downing Street: "Nato is looking at what further requirements there are and Nato and Nato countries have got a duty to respond to that."

He said it was important the "whole of Nato regards this as their responsibility".

"We should never forget that the reason why our troops are in Afghanistan, along with other Nato countries, is because out of Afghanistan came the terrorism of 9/11."

The US ambassador to Nato, Victoria Nuland, told the BBC: "What we are looking to do is to put more forces in so that we can turn the tide faster. The issue here ... is the fighting capability and the fighting willingness of all allies."

US secretary of state Condoleezza Rice said on Tuesday that Afghanistan "could come back to haunt us" if the west once again allowed it to become a failed state.