There have been mounting attacks
against US soldiers (file)
An army statement said an Apache helicopter crashed while supporting combat operations in the southeast sector of the country.
In a statement from Bagram Air Base, officials said the crash was not caused by hostile fire.
The incident is under investigation. No details were revealed of the operation the helicopter was supporting. A US-led coalition of about 11,500 troops is currently searching for alleged Taliban and al-Qaeda remnants in the country.
Sporadic violence continues to take place across the country.
Three Afghans were killed and two others wounded when troops loyal to rival regional commanders clashed in the southern Afghan district of Spin Boldak near the Pakistan border, said officials.
The casualties included an Afghan interpreter with US forces, who was trapped in the crossfire. The clash between forces of Afghan army commanders Abdul Razzak Panjsheri and Fida Mohammad erupted late on Monday over control of a checkpoint.
The shooting came to an end several hours later after US troops in the area intervened and rounded up about a dozen Afghan soldiers.
Residents said tension had been mounting in the area since the government appointed Panjsheri as commander of Spin Boldak last year, replacing Fida who had been sent to Takhta Pul district, about 35 kilometres away.
Meanwhile, a convoy of four trucks, carrying fuel for US-led forces was ambushed by unknown assailants in the southeast sector of the country.
There were no casualties, said US military officials.
In other developments, Afghan government forces killed four suspected Taliban fighters and captured at least four others in a gun battle in the southern Afghanistan area of Arghasan late on Monday.
About 150 Afghan troops were carrying out a search operation in the area bordering Pakistan.