KABUL, June 12: Four men have been arrested following the shocking murders of 11 Chinese construction workers in Afghanistan but mystery remains as to who masterminded the brutal attack.

China's official Xinhua news agency reported that four people had been detained over the killings, news confirmed on Saturday by Kunduz police chief Mutalib Bek.

According to the governor of Kunduz province, Mohammed Omar, two of the Afghans arrested are believed to be loyal to warlord Gulbuddin Hekmatyar.

"One was... a former Hezb-i-Islami who had joined the Taliban," he said.

"And the other who has been arrested by Baghlan (police) is Noor Mohammed, also an ex-Hezb-i-Islami commander."

Omar said Noor Mohammed had also joined the Taliban when northern Afghanistan fell to the militia in 1997.

Hezb-i-Islami is loyal to wanted warlord and former Afghan premier Gulbuddin Hekmatyar and has links with Taliban fighters.

The group, which is thought to cooperate with Taliban and other militants, is believed to have been behind attacks against foreigners and Afghan and Western soldiers in the past.

The Taliban militia has denied responsibility for the killings which occurred in the early hours of Thursday as 100 Chinese engineers, labourers and managers slept in tents pitched on a plain in northeastern Kunduz province, some 35 kilometres south of the provincial capital of the same name.

"We deny the accusation of killing the Chinese workers in Kunduz province of Afghanistan," Abdul Latif Hakimi, who claims to represent the ousted militia, said by telephone from an undisclosed location.

Mr Hakimi said the deaths "should not have happened".

The US military, which leads some 20,000 international troops in the country, said the attack, along with the killing of five aid workers with Medecins Sans Frontieres in the north earlier this month, was not necessarily linked to Taliban, Al Qaeda or Hezb-i-Islami militants.

"Those are two attacks that we have not necessarily attributed strictly to anti-coalition militia," Lt Col Tucker Mansager of the US Army said.

"It's hard to say conclusively that anti-coalition militia activity has spread to the north and northwest," he added.

Despite the arrests, Omar said it was possible the attack had been prompted by rivalry between local commanders intent on securing lucrative road building contracts. "It is a possibility," he said.

However, it was more likely an assault coordinated with "Taliban and Al Qaeda involvement who are still active and are able to carry out such attacks to destabilize the region".

Local police were also unsure as to why the Chinese, along with one Afghan police guard, were cut down by machinegun fire as they slept in tents pitched inside a building site set back some 200 to 300 metres from the road.

The killers appeared to know where to direct their fire, the group of 20 who were armed with machineguns had attacked the most crowded of the tents, according to an eyewitness.

Seven of the eight people in this first tent died and one was wounded.

Most of those killed had only arrived in the area, some 200 kilometres north of Kabul, the day before.

A spokesman for President Hamid Karzai, in the United States after attending the G8 summit and the funeral of former US president Ronald Reagan, said the government could not say who was responsible for the attack.

"We still say whoever it was, it is the enemies of Afghanistan, and it's people who are against reconstruction," spokesman Khaleeq Ahmad said from the US. "We can't really say who."

Omar said he was expecting a delegation from the Chinese construction firm to visit the province to discuss the return of the road workers after the scene was left deserted after the attack.

Kunduz was one of the last pockets of Taliban resistance following the 2001 US-led invasion. -AFP