An American helicopter has crashed inside the Sarabagh military base in Khost province in southeast Afghanistan, on Thursday, one day after a bomb attack killed 21 people in the province.

Local sources said that the US military helicopter went down in Khost and burst into flames.

NATO declined to provide details about the type of helicopter or its mission and there are no words about the possible casualties and the cause of the crash.

But the US-led foreign troops' convoys and aircraft have repeatedly come under fire from the Taliban militants this year.

The US embassy in Afghanistan confirmed on Wednesday that three US-led foreign forces along with their Afghan translator were among the 21 people who were killed on Wednesday.

The casualties came after a bomber riding a motorbike on Wednesday attacked a joint Afghan-NATO convey passing through khost.