At least a dozen Islamic militants wearing police uniforms shot to death a Pakistani and 10 foreign tourists, including an American, who were visiting one of the world's highest mountains in a remote area of northern Pakistan that has been largely peaceful, officials said.
The shooting was one of the worst attacks on foreigners in Pakistan in recent years and is likely to damage the country's already struggling tourism industry. Pakistan's mountainous north - considered until now relatively safe - is one of the main attractions in a country beset with insurgency and other political instability.
The local branch of the Taliban took responsibility for the killings, saying it was to avenge the death of a leader killed in a recent US drone strike.
The 10 foreigners who were killed included two Chinese, one Chinese-American and one Nepalese, said Attaur Rehman, home secretary in the Gilgit-Baltistan area where the attack took place. The other six have not been identified. One Pakistani was also killed, Rehman said.
Matt Boland, acting spokesman at the US Embassy in Islamabad, confirmed that a US citizen was among the dead, but could not say whether it was a dual Chinese national.
"The US Embassy Islamabad expresses its deepest condolences to the family and friends of the US citizen and the other innocent tourists who were killed in the northern areas of Pakistan," Mr Boland said in a statement sent to reporters.
Pakistan's interior minister, Chaudhry Nisar Ali Khan, said earlier that nine foreigners and one Pakistani were killed. He said the dead included five Ukrainians, three Chinese and one Russian. One Chinese tourist was wounded in the attack and was rescued, said Khan. It is unclear what caused the discrepancy between the two accounts.
The attack took place at the base camp of Nanga Parbat, the ninth highest mountain in the world at 26,660ft. Nanga Parbat is notoriously difficult to climb and is known as the "killer mountain" because of numerous mountaineering deaths in the past.
The gunmen were wearing uniforms used by the Gilgit Scouts, a paramilitary police force that patrols the area, said the interior minister. The attackers abducted two local guides to find their way to the remote base camp. One of the guides was killed in the shooting and the other has been detained and is being questioned, said Mr Khan.
"The purpose of this attack was to give a message to the world that Pakistan is unsafe for travel," said the interior minister in a speech in the National Assembly, which passed a resolution condemning the incident. "The government will take all measures to ensure the safety of foreign tourists."