KABUL, Afghanistan - NATO forces on Tuesday launched an airstrike against a group of private security guards who were contracted to protect military supply convoys along an eastern Afghan highway, killing one of the guards, Afghan police and the company said.

NATO confirmed that an airstrike was called in by forces in Ghazni province, but said its initial reports suggested the strike was on "suspected insurgents."

The international coalition said it authorized the strike after its forces observed the suspected insurgents setting up an ambush site in Gelan district -- activity that was confirmed by the air weapons team. They later found several machine guns, a rocket-propelled grenade and four AK-47 assault rifles.

Afghan officials said there were no insurgents involved.

"The Watan Risk guards came under attack on the road," said Zirawer Zahid, the Ghazni police chief. He was referring to Watan Risk Management, a private company that supplies guards for convoys, offices and international organizations.

Zahid said the strike killed one guard, lowering the death toll from five that he had given previously. Zahid said he was going off reports from the company and they had lowered the death toll.

A representative for Watan confirmed that one of their guards had been killed and another five wounded when they came under attack while moving from one checkpoint on the road to another.

"Our guards are all along this road. If we aren't here, no supply convoy can reach its destination. I don't know why the Americans targeted us," said Qudartullah Khan, who oversees Watan's operations in southeast Afghanistan. He shouted into the phone, letting go a barrage of insults at the international military coalition that contracts Watan to protect the road.

"We are constantly under threat from militants in this area, and now the Americans are also targeting us?" he said. Five of his employees were detained by American forces, he said. He explained that they originally gave a higher death toll because they thought the five who are in U.S. custody had been killed.

Both Zahid and NATO said there were no reports of a convoy in the area. Afghan and international officials had previously said the airstrike was called in by a convoy that was under attack.

Also Tuesday, a NATO service member was killed in a pre-dawn bomb attack in the east. There were no further details on the attack or the nationality of the deceased.

More than 150 international service members have been killed so far this year in Afghanistan.

The war in Afghanistan has continued uninterrupted following Monday's deadly strike against al Qaeda leader Osama bin Laden in neighboring Pakistan. Both U.S. officials and their Afghan counterparts have said that there is still a powerful terror network to fight in Afghanistan even after bin Laden's death and that their military strategy remains unchanged.