In a separate incident, two soldiers from the US-led force were wounded when an explosion ripped through their vehicle close to the border town of Shkin.

The helicopter crashed Sunday near the military base in Bagram. US authorities said the cause of the incident was as yet unknown.

"The cause of the crash is unknown and under military investigation," US Central Command said in a statement, Reuters reported.

It said the troops aboard the downed helicopter were supporting Operation Mountain Resolve.

Border strikes

The town of Shkin, located near the border with Pakistan has been a major trouble spot for the US-led force of 11,500 troops, with soldiers coming under frequent and occasionally deadly attack from suspected fighters from Afghanistan's ousted Taliban and the al-Qaida network that it sheltered.

Two years after US forces toppled the Taliban, there  are still al-Qaida operatives believed to be active along the Afghan-Pakistan frontier and the Taliban is regrouping.

The Taliban on Sunday called on Afghans to unite against US forces on their soil.