BAGHDAD — Bombings and shootings ripped across Iraq on Monday, killing at least 103 people in the deadliest day this year. The coordinated attacks in 13 cities sent a chilling warning that al-Qaida is slowly resurging in the security vacuum created by a weak government in Baghdad and the departure of the U.S. military seven months ago.

Though there was no immediate claim of responsibility, the leader of al-Qaida in Iraq declared on Sunday a new offensive aimed at sowing instability across the country.

Iraqi militants have kept up a steady drumbeat of deadly attacks since the U.S. pulled out in December, ending nearly a decade of war. They have sought to deepen the chaos created by the deepening sectarian political crisis that pits Sunni and Kurdish leaders against Shiite political powers. The latest violence bore most of the hallmarks of al-Qaida: the bombings and shootings all took place within a few hours of each other and struck mostly at security forces and government offices — favorite targets of the predominantly Sunni militants.