Afghanistan's Taliban insurgents said on Thursday they were suspending peace talks with the United States because of the "shaky, erratic and vague" U.S. position.
U.S. and Taliban negotiators were believed to have had preliminary contacts aimed at establishing an office for the Taliban in the Gulf state of Qatar to launch peace negotiations.
Even though substantial talks have yet to begin, the Taliban announcement will dent hopes of a negotiated settlement to the more than a decade-long war in the run-up to the withdrawal of foreign combat troops at the end of 2014.
"The Islamic Emirate has decided to suspend all talks with Americans taking place in Qatar from (Thursday) onwards until the Americans clarify their stance on the issues concerned and until they show willingness in carrying out their promises instead of wasting time," the group said in a statement.
The Taliban also said talks with the government of President Hamid Karzai were pointless and none had taken place.
The announcement came days after an American soldier was accused of slaughtering 16 Afghan civilians in the south.
The killings in Kandahar province on Sunday have raised questions about Western strategy in Afghanistan and intensified calls for the withdrawal of foreign combat troops.
Earlier on Thursday, a senior U.S. commander defended moving the American soldier accused of the killings to a military detention centre in Kuwait, saying it would help ensure a proper investigation and trial.
Furious Afghan civilians and members of parliament have demanded the staff sergeant be tried in Afghanistan over the shooting, one of the worst of its kind since U.S.-backed Afghan forces toppled the Taliban in late 2001.
Karzai called on NATO-led forces to move out of all Afghan villages in response to the shooting.
U.S. Defense Secretary Leon Panetta, in Kabul on a two-day visit to try to soothe Afghan anger, discussed the massacre with Karzai at his heavily guarded palace and faced demands from the Afghan leader that any trial be transparent.
"I assured him first and foremost that I shared his regrets about what took place. I again pledged to him that we are proceeding with a full investigation here and that we will bring the individual involved to justice. He accepted that," Panetta told reporters.
Tension has risen sharply since the killings and the burning of copies of the Koran at the main NATO base in the country last month, adding urgency to Panetta's visit.