American aircraft have killed nine Afghan soldiers in an accidental attack on an army post – the latest in a string of deadly mistakes involving Western forces in Afghanistan.

Afghan officials said that the attack happened overnight on Tuesday in the eastern province of Khost. “Nine have been martyred, three wounded, one critically, in the attack by international forces,” said General Zaher Azimi, a spokesman for the Defence Ministry.

The ministry condemned the attack and said that such incidents would weaken the spirit of the Army, which is trained mostly by US troops. The US military said that its forces “may have mistakenly killed and injured” Afghan soldiers. “As a coalition convoy was returning from a previous operation, they were involved in multiple engagements. As a result of the engagements, soldiers were killed and injured,” it said.

“Initial reports from troops on the ground indicate that this may be a case of mistaken identity on both sides.”

According to Lutfullah Babakarkheil, the local district governor, US attack helicopters levelled the army post in Dowa Manda district.

Arsala Jamal, the governor of Khost province, told The Times that US forces were in the area to put Taleban militants on the defensive during voter registration for the presidential elections next year.

The increasing number of incidents involving US aircraft hitting the wrong target has strained the coalition’s relationship with the Government. After one of them last year, President Karzai wept in public as he called on Western forces to take greater care. Previous incidents have affected civilians or police units, with the Army and US military generally coordinating their operations successfully. Colonel Mohammad Gul, spokesman for the 203rd Corps of the Afghan Army, said: “This is the first time the US forces have mis-targeted [the Army] in the eastern region.”

In August US forces mistakenly killed up to 90 civilians in a village in the west of Afghanistan after they were given misleading intelligence by feuding tribesmen.

In July US aircraft bombed a double wedding celebration in Nangarhar province, killing 47 people, including both brides. The same month US aircraft bombed a civilian truck in Kunar province, killing 15 people including Afghan medical staff working for a Western aid agency.

On Monday British commanders in Helmand admitted that civilians were killed during an operation close to the provincial capital. Local people say that up to 25 villagers were killed.

The United Nations estimates that 393 civilians died in Western airstrikes in the first eight months of 2008. Nato sources estimate 161 civilian deaths.

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