Iraq is preparing a “major attack” on militant-held Fallujah, a senior official said Sunday, spelling another assault for the city west of Baghdad where US forces repeatedly battled insurgents.

Washington said it would help Baghdad in its fight against Al-Qaeda-linked militants but that there would be no return of US troops, and Iran on Sunday also offered assistance.

The takeover of Fallujah and parts of Anbar provincial capital Ramadi, farther west, is the first time militants have exercised such open control in major cities since the height of the bloody insurgency that followed the US-led invasion of 2003.