Two US crew members were killed when a US helicopter crashed on Wednesday outside the western Iraqi city of Ramadi, the US military said in a statement.

An AH-1W Super Cobra went down near Ramadi at about 8:10 a.m. ( 0510 GMT), killing two crew members, the statement said.

"The incident occurred while a two-men crew was flying in support of security and stabilization operations," it added.

The brief statement did not say what caused the crash but said the incident was under investigation.

However, witnesses from Ramadi said the helicopter crashed in Albu-Ubaid area east of the city during clashes in the area.

Ramadi, a Sunni-dominated city some 100 km west of Baghdad, has long been an insurgent stronghold.

Source: Xinhua