CASTEAU, Belgium - NATO's top commander renewed an appeal Tuesday for allies to fill gaps in the international military force in Afghanistan, warning that the failure to send reinforcements was weakening the mission and jeopardizing the lives of soldiers fighting Taliban insurgents.

"We do not have adequate forces,'' Gen. John Craddock told reporters. "It makes accomplishing the mission that more difficult. It places every NATO soldier there at greater risk.''

Hours earlier, a Senate committee in Canada said the government should a consider withdrawing from Afghanistan unless NATO allies deliver additional troops.

Canada's 2,500 troops play a key role in the front-line southern provinces and have suffered relatively high casualties. Craddock said any decision to pull them out would create a "terrible situation.''

Taliban guerrillas have proven to be a much tougher foe than the alliance expected in 2003 when they deployed their first contingent of peacekeepers to Kabul. Last year, fighting surged to unprecedented levels and commanders have warned that even fiercer combat could be expected if the insurgents launch a spring offensive against the Kabul government.

Politicians in Canada, Britain, the United States and other countries with troops in the volatile south have been irked by the reluctance of some European allies to commit extra forces to the 35,500-strong NATO force, and in particular to allow their troops to be deployed to the Taliban's heartland in the south and east.

Speaking at NATO's military headquarters in southern Belgium, Craddock said he was optimistic allies would come forward with additional contributions in the coming days and weeks.

However, a meeting of NATO defence ministers last week in Seville, Spain, produced only small offers.

Lithuania, which already has 130 troops in Afghanistan, offered to send an unspecified number of special forces.

Germany plans to provide six Tornado reconnaissance jets; Italy a transport plane and some unmanned surveillance aircraft; Spain also said it would send four unmanned planes and more instructors to help the Afghan army.

Craddock said such offers should not be overlooked, insisting that securing the right sort of specialized troops and equipment was more important than simply pouring in more manpower.

"Sometime 15 is as important as 1,000,'' he said.

He also said the decision last month by the United States to extend the tour of more than 3,000 of its soldiers has given the force a much-needed mobile reserve. However, he said the force was still about seven per cent short of full strength, needing more ground manoeuvre units, transport planes and helicopters and crucial "enablers'' such as airport managers, intelligence and surveillance planes.

He declined to give exact numbers, saying that could give important information to the Taliban, but officials at the meeting in Seville said NATO was looking for up to 2,500 additional ground troops to take the fight to the insurgents in the spring and keep a closer watch on the border with Pakistan.

Craddock said additional troops were needed essentially to ensure NATO is able to maintain a permanent presence in Taliban strongholds that are brought under international control so allied units could launch "quick impact'' reconstruction projects aimed at winning over local support.

"There has to be a coherent, simultaneous effort to secure and stabilize,'' he said in reply to French and German doubts raised in Seville about the need for more troops. "You can't get long term development and reconstruction without security.''

Craddock said the high level of casualties sustained by the Taliban in clashes with NATO last year, made it unlikely they would seek a frontal confrontation this spring.

Instead, he noted they had returned to hit-and-run tactics with an increase in the use of roadside bombs.

He said such improvised explosive devices used by the insurgents were becoming more sophisticated, but were not yet as powerful as armour-piercing bombs used in Iraq which the U.S. military this week claimed to have traced to Iran.