The raid occurred 35km south of the northern city of Kunduz, until now deemed a secure area as Islamist fighters concentrate their attacks in Afghanistan's south and east.

The attack on the Chinese workers comes despite a major US-led offensive into former strongholds of the ousted Taliban government.
 
The provincial governor blamed the raid on anti-government forces bent on destabilising President Hamid Karzai by attacking foreign and Afghan troops as well as aid and reconstruction workers ahead of landmark elections in September.

The Taliban, the main guerrilla group opposed to Karzai's government, denied responsibility. "We were not behind this, we have not done this," spokesman Hamid Agha told Reuters.

The raid was another blow for Karzai, who is visiting the United States and faces growing instability that is undermining vital assistance missions and reconstruction in the war-shattered country of 28 million people.

"It was carried out by the enemies of Afghanistan," said Kunduz governor Muhammad Umar, a referene to the Taliban, their allies in al-Qaida and forces loyal to renegade warlord and former prime minister Gulb al-Din Hekmatyar.

Chinese condemnation

China condemned the killings as a "brutal terrorist act" but said it had no plan to pull its workers out of the country.

The Taliban appear to be widening
their theatre of operations

"The Chinese side will not yield to any form of terrorism," Foreign Ministry spokesman Liu Jianchao said.

Attacks such as Thursday's on Chinese overseas have been rare. But a car bomb exploded at one of neighbouring Pakistan's biggest construction projects in May, killing three Chinese technicians and wounding 11 people.

Liu said the ministry had also summoned the Afghan ambassador and called for an investigation into the attack and for the assailants to be brought to justice.
 
Hundreds of Chinese construction workers are working in Afghanistan, including more than 120 in Kunduz employed on a road paving project for a Chinese company that is being funded by the World Bank.

Major offensive

Meanwhile, US-led troops carried out sweeps of former Taliban strongholds in Afghanistan on Thursday as part of an offensive aimed at stemming a spiral of violence in the lead-up to
September elections. 
  

US marines are spearheading a
push into opposition strongholds

"The operation in the (south central) area is still going on," the military spokesman for southern Afghanistan, General Abd al-Wasay, told AFP.
 
More than 20 anti-government fighters were killed in action and eight were captured on Wednesday, US army spokeswoman Master Sergeant Cindy Beam said on Thursday.

The latest operations are the result of occupation troops - led by around 2200 US marines - battling in former heartlands of the toppled Taliban regime, which include the neighbouring provinces of Uruzgan and southern Kandahar.

Violence spreads

Anti-government forces have been most active in their old strongholds in the south and east. But an attack in the northwest last week that killed three foreigners and two Afghans, and Thursday's Kunduz raid, have raised concern that the fighting is spreading.

At least 15 Pakistani security personnel were also reportedly killed on Thursday while fighting al-Qaida-linked guerrillas in a remote tribal region bordering Afghanistan.

More than 200 NATO-led German peacekeepers are based in the provincial capital of Kunduz. The wounded and dead Chinese were taken to a German-run hospital in the town, about 250km north of Kabul.

Manoel de Almeida e Silva, spokesman for the United Nations in Afghanistan, said voter registration sites in Kunduz had been closed, and UN road missions in and out of the province were suspended.