An Afghan defense official condemned the latest "friendly fire" deaths, which came at a time when international troops are trying to improve coordination with Afghan security forces in hopes of handing over more security to them nearly nine years into the war. Three American soldiers were also reported killed Wednesday in a roadside bomb in the south.

The Afghan soldiers were launching an ambush before dawn against insurgents reportedly on the move in Ghazni province when NATO aircraft began firing on them without warning, Afghan Defense Ministry spokesman Gen. Mohammad Zahir Azimi said.

Five Afghan soldiers died and two more were wounded in the airstrike in Ghazni's Andar district, he said.

"This is not the first time such an incident has happened, but we wish that at least this would be the last one," Azimi said.

NATO spokesman Josef Blotz confirmed the botched airstrike. He said he regretted the Afghan National Army deaths, telling a news briefing that a joint investigation has been launched.

"The reason for this is perhaps a coordination issue," Blotz said. "We were obviously not absolutely clear whether there were Afghan national security forces in the area." He extended the personal condolences of US Gen. David Petraeus, the newly arrived commander of NATO forces in Afghanistan, to the families of the victims.

The Afghan soldiers' deaths at the hands of their allies was another setback in the US-led force's goal of training and coordinating with the Afghans, one of the cornerstones of its counterinsurgency strategy.

NATO is counting on the strategy to beat back the insurgents' recent gains, nearly nine years after US-backed forces toppled the Taleban's hard-line Islamist regime. The aim is to win over the population by limiting Afghan casualties while securing new areas, eventually turning control over to local army and police and allowing foreign troops to withdraw.

Violence has been increasing across Afghanistan, coinciding with the arrival of thousands of American soldiers for a new push to try to establish Afghan government control in the south, one of the Taleban's strongest areas of influence.

On Wednesday, NATO said three American troops were killed by a roadside bomb in the south Tuesday. It did not identify them or give any other details.

Last month was the deadliest for international forces since the war began, with 103 killed, including 60 Americans.
 

Meanwhile, UK Defense Secretary Liam Fox said on Wednesday that British troops are to withdraw from the Sangin region of southern Afghanistan.

Sangin, a valley in the north of the Helmand province, has been one of the deadliest areas for British forces, accounting for about a third of the 312 British dead in the nine-year-old war.

The United States will take over responsibility for the area in a reconfiguration of NATO-led forces, Fox told parliament. The British troops will focus on operations in central Helmand.