Rice, speaking en route to London where she will discuss strategy on Afghanistan with British leaders, called for the quick appointment of an envoy to coordinate what she termed NATO's bumpy mission.

"It is true, and we have made no secret about it, that there are certain allies that are in much more dangerous parts of the country," Rice told reporters travelling with her.

"We believe very strongly that there ought to be a sharing of that burden throughout the (NATO) alliance," said Rice, adding she did not wish to denigrate the contribution of allies.

Some NATO countries have bristled at public criticism from Washington over the refusal of a number of alliance members to position their forces in the more dangerous south of Afghanistan to fight Taliban insurgents.

Germany, for example, under its parliamentary mandate can send only 3,500 soldiers to the less dangerous north as part of the 42,000-strong NATO mission.

That means most of the fighting against the Taliban is shouldered by Canada, Britain, the United States and the Netherlands. They all want others to contribute more.

The Taliban, ousted from power by a U.S.-led invasion in 2001, fought back strongly last year.

ENVOY

Western efforts in Afghanistan have been fragmented and Rice said she hoped a new international envoy could be appointed soon to coordinate this work.

In January, Afghan President Hamid Karzai rejected politician Paddy Ashdown for the job.

"We want to be very clear that this is a sovereign Afghan government and it has to take its own decisions, but it has a heavy reliance on international support," said Rice.

"It is important to move ahead on an envoy as soon as possible," she said.

Rice, due to meet Prime Minister Gordon Brown and Foreign Secretary David Miliband, said she believed another European was likely to get the post.

Part of Rice's London visit is to smooth relations after U.S. Defence Secretary Robert Gates upset many close allies, including Britain, when he questioned the preparedness of some NATO members for counter-insurgency in southern Afghanistan.

"It is bumpy and there is a lot of maturing that the alliance is having to do ... Frankly, counter-insurgency is really hard for any traditional military, let alone (NATO)," said Rice.

The United States has 29,000 military personnel in Afghanistan, about half of them attached to the NATO mission. Washington plans to send an additional 3,200 troops and hopes this will encourage others to do the same.

Canada has said it would pull out its forces early next year if other NATO countries did not send in more.

Two U.S. non-governmental reports last week said Afghanistan risked becoming a failed state and a haven for global terrorism without new U.S. and international efforts to win the battle against the Taliban.

Asked for her assessment, Rice said there were "challenges" and that the Taliban had "by no means been defeated".