KABUL, Afghanistan - Taliban fighters killed 15 Afghan guards working for a private security company who were guarding a convoy of fuel tankers in western Afghanistan, an official said Tuesday. Six Taliban were killed in the ensuing fight.

Several militants also were killed in airstrikes and a subsequent operation by U.S.-led coalition troops in the country's south on Monday, the coalition said.

Between six and eight vehicles of a private security company were guarding a convoy of fuel tankers when the Taliban attacked early Tuesday, said Farah province Gov. Muhaidin Baluch.

Fifteen guards were killed and five were wounded, Baluch said. One fuel tanker was set on fire, he said.

Baluch said the guards worked for USPI -- Houston-based US Protection and Investigations. USPI officials did not immediately return telephone messages seeking comment left at the company's Houston headquarters. They could not be reached for comment at its offices in Kabul.

However, two USPI employees contacted by The Associated Press, who asked not to be identified because they were not authorized to talk to the media, said the company's guards were not involved. One employee said Afghan officials in the south tend to identify all security companies as USPI, even when they are not.

Gen. Khail Buz Sherzai, the provincial police chief, said officials were not sure of the name of the security company.

Baluch said the tankers were traveling from the western city of Herat to a military outpost in Lashkar Gah, the provincial capital of Helmand province, the region that has seen the heaviest fighting in Afghanistan this year.

Elsewhere in Farah, fighting between police and militants left two of the militants dead, said Gen. Khail Buz Sherzai, the provincial police chief.

In southern Afghanistan, a U.S.-led coalition airstrike on a Taliban commander and subsequent operation in Helmand province killed several militants Monday, the coalition said. The strike targeted a Taliban commander involved in the movement of foreign fighters and suicide bombers, it said.

More than 6,300 people, mostly militants, have been killed in insurgency-related violence in Afghanistan this year, according to an AP count based on official figures. The country has also seen a record number of suicide bomb attacks -- more than 140 -- in 2007.

An e-mailed message purportedly from Mullah Omar, the fugitive leader of the Taliban, meanwhile, dismissed the takeover last week of Musa Qala by Afghan, British and U.S. troops as only a propaganda victory. The southern Afghan town had been in militant hands since February.

"They have still not occupied all of Musa Qala," Omar said in an emailed message sent through Taliban spokesman Qari Yousef Ahmadi, in apparent recognition of the Muslim holiday of Eid. "Only the center of the town with a few shops are under their control and they think that is a great victory."

The message's authenticity could not be confirmed. Fighting is still taking place on the outskirts of Musa Qala.

Omar also said Taliban leaders were not holding talks with the government of President Hamid Karzai.

The Danish army said an investigation had revealed that two of its soldiers were accidentally killed by British friendly fire during an operation in September against Taliban fighters in southern Afghanistan.

The soldiers were killed Sept. 26 in the Upper Geresk Valley of Helmand province during an operation that involved another unit under NATO's International Security Assistance Force. A third Danish soldier was slightly wounded.

Peter Otken, the head of Denmark's military prosecutors, said an investigation had revealed that the British forces, under whom the Danish unit served, fired missiles at what they thought were Taliban positions. Both Danes died after being hit by shrapnel, according to a four-page statement.

Denmark has some 600 troops in Afghanistan, most of them based in the volatile Helmand province. Nine Danish soldiers have been killed in Afghanistan since Denmark joined the U.S.-led coalition in 2002.

British Brig. Andrew Mackay, commander of Task Force Helmand, said the British army could not comment until its investigation was complete.