President Bush's appeal was the latest in a US drive to persuade reluctant Nato allies to take on a larger role in combating a resurgent Taleban and their al Qaeda allies in the most volatile parts of the country.

US officials are disappointed at the meager results of their pressure campaign so far and warn that Nato's credibility could be at stake. The issue is expected to figure prominently at Nato's April 2-4 summit in Bucharest.

'I am going to go to Bucharest with the notion that we're thankful for the contributions being made and encourage people to contribute more,' President Bush said at a joint news conference with Danish Prime Minister Anders Fogh Rasmussen at the president's Texas ranch.

President Bush stopped short of naming the allies he believes should commit more troops while acknowledging 'certain political constraints on certain countries.' But he insisted, 'My administration has made it abundantly clear we expect people to carry a heavy burden if they're going to be ... in Afghanistan.'

Standing shoulder to shoulder with President Bush, Mr Rasmussen agreed, 'We need more troops in Afghanistan ... I feel confident that we can convince partners to contribute with more troops than today.' Denmark has nearly 800 troops mostly in southern Afghanistan.

Pressure on France, Germany
The United States wants France, Germany and other allies in particular to deploy troops to the south of the country where the fight against Islamist militants has been toughtest.

Britain, Canada, Poland and others have backed the US demand. In what would be a major blow to the 43,000-strong Nato mission, Canada has warned that it will not renew its deployment past 2009 unless other Nato allies come up with 1,000 troops to support its operation in Kandahar.

Germany, under pressure from Washingtion, has recently softened a longstanding insistence that it cannot exceed a self-imposed limit of 3,500 troops in Afghanistan, and no longer excludes reinforcements this year.

France has also signalled a willingness to send more troops, but appears to be balking about sending them south.

A senior Bush administration official, briefing reporters on Friday, said the United States expects 'helpful' troop contributions to come out of the Bucharest summit, but that any increase would be within limits.

US Defence Secretary Robert Gates said during a visit to Germany last month that the Nato alliance was at risk if it became split between members willing and unwilling to fight.

The United States has 29,000 troops in Afghanistan, split between those assigned to the Nato mission and forces operating independently, and plans to send an additional 3,200 Marines in April. -- REUTERS