The Marines have also eliminated insurgent positions and strongholds, and are stabilizing the region, CNN reported, quoting Col. Peter Petronzio, commander of the 24th Marine Expeditionary Unit.

The fighting against the Taliban has been concentrated in the Garmsir region in Helmand province, a major opium poppy growing area whose crop has helped finance the insurgency.

"The Taliban proved that they wanted to fight for Garmsir, and we took the fight to them, inflicted very serious casualties," Petronzio said. Those killed "is somewhere beyond 400," he said after talking with a local official, the report said.

The commander said the Marines have been involved in counterinsurgency since April 28, the report said.

"I wouldn't say that Garmsir is secure but it is stable. We are continuing to clear the area. Insurgents are still there but they are not engaging with us as they once did," he said.