KABUL, Afghanistan (AP):

A United States warplane mistakenly bombed British troops after they called for air support in Afghanistan, killing three soldiers and wounding two others in an accident that could reignite debate about America's heavy use of air power.

British officials said they were investigating the error, the first 'friendly fire' incident between the two forces in Afghanistan. Similar mistakes by U.S. troops in Iraq have led to the deaths of 12 British servicemen since 1990.

The troops were patrolling north-west of Kajaki, a militant hot spot in southern Helmand province on Thursday evening when they were attacked by Taliban fighters, Britain's Ministry of Defence said in a statement.

"During the intense engagement that ensued, close air support was called in from two U.S. F-15 aircraft to repel the enemy. One bomb was dropped and it is believed the explosion killed the three soldiers," it said.

The military did not name the soldiers, from 1st Battalion, The Royal Anglian Regiment. The wounded soldiers were both seriously injured, an army spokesman said.

British Defence Secretary Des Browne declined to speculate on the cause, and said he did not want "to get into a situation where we are blaming each other" over the incident.