A NATO airstrike killed at least five private security guards Tuesday who were apparently involved in guarding a supply convoy for international troops, Afghan police said.

NATO confirmed that an airstrike was called in by forces in Ghazni province in eastern Afghanistan, but it its initial reports suggested the strike was on insurgents.

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

NATO said there were no reports of a convoy in the area. The alliance had previously said the airstrike was called in by a convoy that was under attack.

Afghan officials said there were no insurgents involved.

"This morning, there was some sort of incident between an American convoy and security guards from Watan Risk," said Zirawer Zahid, the police chief of Ghazni. He was referring to Watan Risk Management, a private company that supplies guards for convoys, offices and international organizations.

Zahid did not have details on what prompted the NATO airstrike, but he said it killed at least five of the Watan guards. Watan could not immediately be reached for comment.

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-Qaida 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 the death of bin Laden and that their military strategy remains unchanged.