ISLAMABAD, August 3, 2008 (AFP) - At least nine mountaineers died near the summit of K2 when a huge chunk of ice sheared off the mountain and hit them, and several more climbers are missing, Pakistani tour operators said Sunday.

Three South Korean, two Nepali, a Dutch, a Serb, a Norwegian and a Pakistani climbers were among those killed when the disaster struck on the notoriously treacherous Himalayan peak, the world's second highest mountain after Mount Everest.

'I can confirm nine dead and three missing,' Nazir Sabir, a celebrated Pakistani climber and chief of Nazir Sabir Expeditions, told AFP.

'Three South Koreans, two Nepali, one Dutch, one Serb, one Norwegian and one Pakistani have been killed,' said Sabir, who scaled K2 in 1981 and Everest in 2000.

'It is the worst tragedy on K2 since 1986, when 12 climbers were killed due to exposure,' he said.

The missing were from France, Pakistan and Austria, Sabir said.

Mohammad Akram, vice president of the company that organised one of the expeditions, told AFP the group was hit by the falling ice as they made their descent on Friday.

An air search had been called in to try to find the missing climbers, he said.

The avalanche apparently struck an area of the mountain known as the 'Bottleneck,' where the South Korean and Nepali climbers died, Akram said.

'Three Koreans and two Nepalis have died at Bottleneck,' Ghulam Muhammad, owner of tour operator Blue Sky Trekking and Travel, told AFP. 'The liaison officer at base confirmed the casualties.'

The pyramid-shaped K2, which sits on the border between Pakistan and China, is considered by mountaineers to be by far the hardest of the 14 summits over 8,000 metres to scale.

Weather patterns in the high-altitude Karakorum range where the mountain is located are also extremely volatile.

The extent of the casualties was still unclear Sunday, with Spanish media reporting up to 11 people may have been swept away by the avalanche, citing a blog linked to an 18-member expedition.

Basque daily Gara quoted Basque climber Alberto Zerain as saying he had reached the summit of K2 on Friday evening but a 'drama' had hit several members of his expedition.

NoritK2 expedition leader Wilco van Rooijen, from The Netherlands, was spotted returning late Saturday, but climbers Gerard McDonnell from Ireland and Hugues d'Aubarede from France were missing, as was Pakistani porter Karim, Akram said.

It was not clear if those missing were part of the three missing cited by Sabir.

Italian climber Marco Confortola had also returned and was suffering from frostbite on his arm, he said.

Sabir said van Rooijen was injured and had been rescued by his fellow climbers at Camp 2 and Camp 3.

Separately, government officials said late Saturday that the Serbian mountaineer Dren Mandic and another unidentified member of his expedition died after falling into a crevasse on K2 last month.

Deputy Commissioner of Skardu town Wazir Ishfaq told AFP the Serbs, who began their climb in June, had informed the authorities of the two casualties on their return.

K2, known in the local language as Chogori or King of Mountains, has a ratio of climbers to deaths of 27 percent, three times that of Everest.

Italian climbers Achille Compagnoni and Lino Lacedelli first scaled the mountain on July 31, 1954. Between that first ascent and 2007, there were 284 successful ascents and 66 fatalities.

Over the years, K2 has claimed the lives of some of the world's most accomplished mountaineers, including Britain's Nicholas Estcourt, Alan Rouse, Julie Tullis and Alison Hargreaves, American Rob Slater and France's Lilliane and Maurice Barrard.