AGHDAD, Iraq, April 10 — A group of armed Iraqi insurgents, their faces masked, claimed on Saturday to be holding 30 foreigners hostage and threatened to kill them unless the United States halted its offensive in Falluja, the Sunni city west of Baghdad.In a film from the Australian Broadcasting Corporation that was shown repeatedly on Arabic television, a masked man representing the group said: "We have Japanese, Bulgarian, Israeli, American, Spanish and Korean hostages. Their numbers are 30." He added: "If America doesn't lift its blockade of Falluja, their heads will be cut off." The tape did not show any...