Militants on Thursday tried to assassinate Afghan President Hamid Karzai, reports quoted the US military as saying.

A rocket was fired at an American helicopter carrying Karzai, but it missed the target by 300 yards, the reports said.

The chopper was readying to land in Gardez, 60 miles south of Kabul, when the rocket was fired. The aircraft immediately turned around and returned to Kabul, US military spokesman Major Mark McCann said.

"The president was not in any imminent danger," McCann said.

It was at least the second apparent attempt on his life since he took office in 2001.