US forces launched airstrikes against suspected militant bases in Fallujah and carried out probing attacks on the city’s outskirts, as they prepared for a major operation in the insurgent bastion that has become the symbol of Iraqi resistance.

US forces are poised for a major assault on the insurgent stronghold of Fallujah, a general said today, as hundreds of British troops reached a base near Baghdad to free American forces to join the onslaught.