"There was shooting," a US embassy spokesman in Kabul said on Sunday. "The British pilot is dead and an American passenger was critically injured." The helicopter went down nearly 60km south of the southern city of Kandahar.
It belonged to US construction company Louis Berger Group Inc, which is overseeing the reconstruction of the Kabul-Kandahar highway.
A man claiming to represent remnants of the ousted Taliban regime immediately claimed responsibility for the attack and told AFP the civilian helicopter had been targeted because it was assisting a US military-run provincial reconstruction team (PRT) in the area.
"It was fired at by PK machine guns and rocket propelled grenades," the spokesman, who calls himself Muhammad Saif al- Adl, said.
"According to our information, all four people on board have died."
Saif al-Adl said the helicopter was attacked because it was helping the PRT build a school in Taloqan district of Panjwayj.
The Kabul-Kandahar highway has been plagued by kidnappings and armed attacks by Taliban armed fighters.
The last helicopter crash in Afghanistan was in November, when an MH-53 transport chopper carrying US troops crashed near the main coalition base in Afghanistan, killing five and injuring seven others.