Nato defence ministers meeting today are not expected to offer any more troops for Afghanistan, despite a plea from military commanders for another 7,500 soldiers, alliance sources said yesterday.

The gloomy prediction on the eve of an informal session of the defence ministers in Vilnius, capital of Lithuania, pre-empted appeals yesterday from Gordon Brown and Condoleezza Rice, the American Secretary of State, for other Nato countries to share more of the burden in Afghanistan.

Dr Rice, who met the Prime Minister and David Miliband, the Foreign Secretary, said: “I do think the alliance is facing a real test here. Our populations need to understand this is not a peacekeeping mission.”

Only a small number of nations had troops in the most dangerous parts of Afghanistan, she said. “We believe very strongly there ought to be a sharing of that burden throughout the alliance.”

The main Nato players in the south are Britain with 7,800 troops, US (3,100), Canada (2,500), The Netherlands (1,600), Denmark (680), and Romania (500). Australia, not a Nato member, has 1,000 troops there.

Emphasising the focus of Taleban activity in the south, Nato sources said that 70 per cent of the insurgent incidents in Afghanistan took place in 10 per cent of the 398 districts, most of them in the south.

Mr Brown told the Commons: “We have 15 per cent of the troops in Afghanistan. We need a proper burden-sharing not only in terms of personnel but also in terms of helicopters and other equipment.”

Germany confirmed that it would send around 200 extra combat soldiers to northern Afghanistan to replace a Norwegian unit, but said that it would not move the troops to the south.

The appeal caused some anger in an already divided alliance. Nato officials said that the constant highlighting of the rifts in the alliance over troop deployments to Afghanistan was undermining all the achievements made over the past year. “These public rifts and talk of crisis in the alliance are doing the Taleban's work for them,” one official said.

“There were never going to be decisions made in Vilnius about more troops for Afghanistan because it's just an informal meeting, but now it will be seen as a failure because no one is expected to come forward with offers,” another official said. The sense of crisis was made worse by news from Ottawa where the Canadian parliament is split over whether Canada's 2,500 troops in Kandahar in southern Afghanistan should be recalled next year. Stephen Harper, the Prime Minister, was reported to be threatening to go to the polls if parliament voted against extending Canada's troop commitment.

Yesterday Britain underlined its commitment in southern Afghanistan by announcing the next two rotations of troops, each to serve in Helmand province in the south for six months: 16 Air Assault Brigade will go out in April, and 3 Commando Brigade, Royal Marines, will follow in October. Each will send about 7,800 troops.

The Ministry of Defence said that the same number of combat troops - as opposed to support units — would be deployed on each rotation. Two Parachute Regiment regular battalions, 2 Para and 3 Para, will form the principal fighting force of 16 Air Assault Brigade. The Parachute Regiment now has only two regular battalions for this type of deployment, because 1 Para has been reassigned and converted into the Special Forces Support Group, to provide back-up to the SAS and Special Boat Service (SBS).

However, the list of units going out in April, released by the MoD yesterday, has underlined the manpower shortages suffered by the main infantry battalions earmarked for Afghanistan. The MoD said that 2 Para and 3 Para were each about 100 men short, and that 60 men from 4 Para which is the Territorial Army support unit, are filling in some of the gaps.

Other units with manpower gaps going out to Helmand province in April include The Royal Highland Fusiliers, 2nd Battalion The Royal Regiment of Scotland, The Argyll and Sutherland Highlanders, 5th Battalion The Royal Regiment of Scotland, and the 1st Battalion The Royal Irish Regiment, all of which are 90 men short.

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