US soldiers came under heavy fire from Taliban militants and called in air strike but helicopters shot wrong targets

This article is more than 6 years old

This article is more than 6 years old

An air strike has killed five US troops and one Afghan soldier in southern Afghanistan, the deadliest friendly fire incident of the war for Nato forces.

Helicopters were called in by US soldiers when they came under Taliban attack after a day's heavy fighting in Zabul province, east of Kandahar, Afghan officials said, but the pilots hit the wrong men.

"We had launched a clearance operation in an area with a high security threat," General Ghulam Sakhi Rughlewanai, the Zabul provincial police chief, said.

"When it was over and we were returning to base the enemy opened fire and [the US troops] asked for air support. The helicopters made a mistake and targeted their own people."

More than 150 police and soldiers, US and Afghan – along with a handful of intelligence officers – had taken part in the mission, which began at 6am and ended a couple of hours after sunset. After they gathered to leave the area, the insurgents attacked again.

Afghan security forces have gone on the offensive against Taliban fighters in advance of 14 June, when the second round of a crucial presidential election will be held. Insurgents have vowed to disrupt the voting, so government troops are trying to create bubbles of security at polling stations.

The deaths, along with one other in eastern Afghanistan, made Monday the bloodiest day for foreign forces since a helicopter was shot down in December 2013, killing six.

Nato forces have officially stepped back from frontline fighting to focus on training Afghan soldiers, and death rates have dropped dramatically.

But some troops still go on operations to help Afghan soldiers in areas where they have weaknesses, including limited intelligence, and sometimes this involves calling in air support. It is one of those teams that appears to have been caught up in Monday's attack.

"We can confirm five International Security Assistance Force service members died in southern Afghanistan yesterday," the ISAF said.

"The casualties occurred during a security operation when their unit came into contact with enemy forces. Tragically, there is the possibility that 'fratricide' may have been involved."

If confirmed, that makes it the deadliest friendly fire incident in Afghanistan for several years, and the worst of the war for foreign troops.

In 2010 German soldiers killed six Afghan troops who were rushing to the aid of other Afghan forces in a fight against Taliban.

The previous worst single friendly-fire incident of the war for coalition soldiers was in 2002, when a US fighter pilot dropped a 500lb bomb on Canadian troops – who were carrying out a live-fire exercise near an old al-Qaida training base – killing four and injuring eight.

Perhaps the most notorious friendly fire incident of the past decade was the 2004 death of American football player Pat Tilman. His family were originally told he had been killed in a Taliban ambush, and did not learn the truth until after he had been buried, causing a public outcry and prompting accusations of a cover-up.

Other attacks within one country's military or between different coalition forces have been a small but recurrent cause of death and injury, including two British soldiers in 2012 and one in 2010.

Sophisticated identifying and communications equipment has cut confusion on the battlefield, one of the leading causes of friendly fire deaths, but the accuracy of weapons targeting has also improved, making any mistake more likely to be lethal.

Another soldier died in eastern Afghanistan on Monday, Nato said, but not from a combat injury. It gave no further details. At least 40 foreign soldiers have died in Afghanistan this year, although the number of dead has fallen dramatically from a peak of more than 700, in 2010.

There are about 50,000 Nato troops still stationed in Afghanistan, but they are scheduled to leave by the end of this year. The US has promised to leave about 10,000 soldiers behind, bolstered by hundreds from allies, if the new president signs a long-delayed security agreement with Washington.