BRUSSELS, Belgium — Afghanistan's U.S.-backed government, tarnished by corruption and unable to control large swaths of its own territory, is rapidly losing the support of ordinary Afghans, Richard Holbrooke, the former U.S. ambassador to the United Nations, said Saturday.

Holbrooke said NATO, which has committed 36,000 troops to Afghanistan, was at risk of losing the war against the Taliban. The United States has deployed an additional 11,000 troops in the eastern border region with Pakistan.

"I can sense a tremendous deterioration in the standing of the government. Afghans are now universally talking about their disappointment with (President Hamid) Karzai. Let's be honest with ourselves ... the government must succeed or else the Taliban will gain from it," he told the Brussels Forum, an annual trans-Atlantic security conference.

Taliban guerrillas have vastly expanded their activities during the past year. Insurgents have now returned to many regions outside their traditional strongholds in the east that were rebel-free since the 2001 U.S.-led invasion of Afghanistan.

Afghan and NATO forces clashed with Taliban militants Saturday in the east and south, killing 21 suspected insurgents, officials said, including 11 who died in a NATO airstrike in Khost province's Alishar district.

NATO-led forces are in the midst of an operation in southern Afghanistan to root out militants in Helmand province's opium-producing heartland.

Separately, a NATO service member was found dead in his barracks Friday, the alliance said in a statement. In eastern Afghanistan, another NATO soldier died and one was injured from non-combat causes Saturday, a second statement said. Neither statement provided further details.

In Brussels, Canadian Foreign Minister Peter Mackay said the fate of the allied operation in Afghanistan — in which 54 Canadian soldiers have died so far — hangs by a thread.

"While I don't want to sound alarmist, I think there is going to be a tipping point unless we are able to stabilize (southern Afghanistan), unless we are able to get on with" building the economy, rule of law and government institutions.

He said Canada has been disappointed by a lack of solidarity within NATO to share the burden of the Afghan operation.

But Daniel Fried, an assistant U.S. secretary of state, said the situation in Afghanistan is not as "dire" as Holbrooke presented it.

"There are some serious challenges (but) efforts are under way to address the problems Ambassador Holbrooke has identified," Fried said.

Holbrooke, who was instrumental in formulating U.S. policy toward the United Nations, Africa, Asia and the Middle East, remains best known for his role as the architect of the 1995 Dayton Peace Agreement which ended the war in Bosnia.

He said the U.S.-financed effort to train Afghan police has produced a force that is corrupt and incompetent.

"I don't want to appear negative, but unless we are honest about the problem we will continue saying year after year that we are making progress, but have lost ground. We all know where that leads," he said.