The visit comes as thousands of American reinforcements pour into the fragile Asian nation in a bid by US President Barack Obama to gain the upper hand in a conflict that commanders say has turned into a stalemate.

Most of the 21,000 additional US troops are heading to the south, a Taleban stronghold and the center of a thriving opium trade that helps finance the insurgency.

Mr Gates is due to discuss the outlook in volatile southern Afghanistan on Wednesday in Maastricht with North Atlantic Treaty Organisation counterparts who have troops in the region. He then heads to Brussels on Thursday for a meeting of alliance defense ministers, the Pentagon said.

With the US force in Afghanistan due to double to about 68,000 by the end of the year, the American military presence - combined with plans to send in US civilian experts - will eclipse the 33,000 other foreign troops now stationed there.

And in the south, the Dutch are due to hand over command there next year to a US officer.

The troop buildup and transfer of command in the south will mean the US military will have a dominant role in shaping the coalition effort, analysts say.

US officials and lawmakers, critical of what they call an unwieldy command arrangement, have spoken of reorganising the Nato-led command structure in Afghanistan to grant top US officers more control over coalition units engaged in combat - but it remained unclear if Mr Gates would push for major changes.

Allied defence ministers are also expected to endorse plans to cut the Nato peacekeeping force in Kosovo by a third in January, possibly freeing up some troops for the Afghan mission.

Lieutenant-General Stanley McChrystal, with years of experience running special operations, is expected to take over soon as commander of US and Nato forces. -- AFP