BAGHDAD - Attacks by five suicide bombers on an Iraqi military base north of Baghdad on Sunday killed at least 15 members of the security forces and wounded 22 others, security sources said.Two of the bombers detonated their vehicle-borne explosives at the gate of Camp Speicher, a former US base outside the Sunni city of Tikrit. Three others detonated their explosives after entering the base, the sources said.Islamic State claimed responsibility for the blasts in a statement distributed by supporters online.