Twelve people were killed on Saturday when militants attacked a police checkpoint north of Tikrit and then detonated a car bomb at the entrance to the city, Iraqi police and military sources said. There was no immediate claim of responsibility for the attack, which is the first of its kind since the city, 150 km (95 miles) north of Baghdad, was retaken from Islamic State in April 2015. One of the militants was killed at the checkpoint after shooting dead four police officers, according to police and sources from Salahuddin Operations Command, which is responsible for security in the area. Two other militants continued about 7 km to the city limits and detonated the explosives in their pickup truck, killing eight people and wounding 23, the sources said.