U.S. negotiation efforts with the Taliban have failed and the United Nations should take the lead to optimise the chances of ending almost 11 years of war, a think tank said on Monday.

In a blow to hopes of a negotiated end to the war, the Taliban suspended talks with the United States two weeks ago after the alleged massacre of 17 Afghan civilians by a lone U.S. soldier and the burning of Korans at a NATO base last month.

"U.S. efforts to negotiate with the Taliban to date have failed and risk further destabilizing the country and the region, and as a result we call for the U.N. Secretary General to intervene and appoint a team of negotiators," said Candace Rondeaux, a senior analyst at the International Crisis Group (ICG).

In a 51-page report, the think tank said the effect of international support for negotiations had been to increase "incentives for spoilers ... who now recognize that the international community's most urgent priority is to exit Afghanistan with or without a settlement."

Calls for a negotiated settlement have grown over the last few years as NATO-led troops battle a stubborn insurgency and Western forces begin drawing down troop levels ahead of a pullout of most soldiers by the end of 2014.

Western officials believe the Taliban's suspension of talks was tactical and reflected internal tension rather than a definitive halt to discussions.

The string of U.S. setbacks has damaged ties with Kabul at a time when Washington is negotiating a pact to outline its future presence in the Asian country.

"The events of the last couple of months ... all point to a major shift in Afghan perceptions of the U.S. role here. It's going to be very difficult for the United States to both facilitate a solution and also be a party to the solution," Rondeaux, the lead author of the report, said.

'MARKET BAZAAR APPROACH TO NEGOTIATIONS'
U.S. objectives in Afghanistan are far more modest than they were in the months following the September 11 attacks, when the West hoped to replace the Taliban with a stable democracy.

Nearly 11 years after the Taliban government was toppled, the United States and its allies continue to face major problems, including insurgent attacks, a weak government and an uncertain future for Western support.

Doubts are also growing about whether the Taliban leadership is willing to defy possible opposition from junior and more hard-core members who appear to oppose negotiations.

"The Afghan government and its international backers have adopted a market bazaar approach to negotiations. Bargains are being cut with any and all comers, regardless of their political relevance or ability to influence outcomes," the ICG said.

The outgoing UK envoy to Afghanistan, William Patey, said on Sunday, however, that in every peace process there were stops and starts, although he did not believe there had been a "strategic" decision yet by the Taliban to make peace.

The Brussels-based group warned that failure to hash out a better approach to a settlement could mean more conflict, especially in the context of national elections set for 2014 in which President Hamid Karzai is barred from standing again.

"If anything, it will be the election that is the proverbial straw that breaks the camel's back in Afghanistan because this is the last term for Karzai constitutionally," Rondeaux said.

"There is a sense of political vacuum, it's not clear at all who will replace him and that means the competition becomes much more intense. Unfortunately political competition in Afghanistan is never peaceful, it is almost always violent."