BAGHDAD—A suicide bomber killed at least 46 people and wounded more than 60 others Tuesday after detonating his explosives amid a crowd of young men congregating for the last day of an army-recruitment drive in Baghdad, the latest in a series of attacks targeting Iraqi security forces.

Police checkpoints, patrols and even traffic cops have been targeted in brazen attacks over the past month in and around Baghdad, underscoring the vulnerability of both the Iraqi government and its security forces just weeks before the end of...