In Washington, top White House officials sought to bolster support for the new strategy, decided on after weeks of high-level talks.

Joint Chiefs of Staff head Adm Mike Mullen said the surge would provide "forces to turn this thing around".

Defense Secretary Robert Gates warned that failure to act against the resurgent Taliban would have "severe consequences" for the US and the world.

Mr Gates, speaking to the Senate Armed Services Committee, said that the first troops would go within weeks. He also backed Mr Obama's goal of beginning to bring them home within 18 months.

Nato leaders are due to meet, with the issue of more troops top of the agenda.

Mr Obama announced on December 1 that he was sending 30,000 more US troops to fight in Afghanistan, taking the total number of US soldiers there to more than 100,000.

Nato Secretary General Anders Fogh Rasmussen says other Nato countries will provide at least 5,000 extra troops, and "probably a few thousand on top of that".

The extent of additional resources coming from Nato allies remains unclear, although European nations have voiced support for Mr Obama's surge.

Britain, Georgia, Poland and Slovakia have all pledged more troops but other nations such as France, Germany, Italy and Denmark are being more cautious.