The meeting of Nato allies in Riga this week has made "significant progress" in bolstering the forces serving in Afghanistan, Tony Blair has said.
The prime minister said commanders would now have 85 per cent of the troops they needed, after several Nato countries dropped restrictions on the deployment of their armed forces.
Leaders of the 26-member alliance also stated in a summit declaration: "Contributing to peace and stability in Afghanistan is Nato's key priority."
Mr Blair told reporters in the Latvian capital: "These have been significant steps in the right direction. Have we got absolutely everything we wanted? Not yet."
Reports suggest that Bulgaria, Spain and Nato-hopeful Macedonia have offered more troops for Afghanistan, while the Netherlands and Romania had lifted all restrictions on where their armed forces are deployed in the country.
Most of the losses in Afghanistan since the US-led invasion in October 2001 have been American, British, Canadian or Dutch, and these countries have been pressing for several months for a greater contribution from other Nato members.
Canada - which has lost 44 lives so far - has promised 1,000 more troops without restrictions, and Denmark and the Czech Republic are also thought to have pledged more.
France, Germany and Italy relaxed their restrictions slightly, and have now agreed that troops can be moved to the most dangerous regions of Afghanistan - notably the south, where about 4,300 troops are based - in the event of an emergency.
Last night, Mr Blair said Nato leaders must send a "clear message" that it was prepared to make the military commitment needed to sustain its mission in Afghanistan.
"This operation in Afghanistan is of crucial importance to our own security. Nato's credibility is at stake here. If we don't succeed in Afghanistan, the whole of our world will be less secure," he said.
Speaking to reporters this morning, he said that the mission in Afghanistan was "obviously not yet won but it is winnable and we are winning". He stressed it was now crucial that Nato countries lived up to their commitments.
There are currently about 5,600 British forces in Afghanistan in support of the UN-authorised, Nato-led international security assistance force (Isaf). The majority are based in the south and 1,300 are based in Kabul, the Afghan capital.