After fleeing their initial target, a checkpoint where four police were shot dead, attackers detonated an explosive-laden vehicle near the entrance to Tikrit, killing eight and wounding many others.
Twelve people were killed on Saturday when attackers targeted a police checkpoint north of Tikrit and then detonated a car bomb at the entrance to the city 7km down the road, Iraqi police and military sources said.
The spokesman for the Salahuddin province police force, Col. Mohammed al-Jabouri, said three militants rammed their explosives-laden vehicles early Saturday morning into the main checkpoint near the town of al-Salam at the province's northern entrance.
Al-Jabouri added that 34 other security officers were wounded.
He said the attacks occurred as the local police chief and head of the provincial security committee were visiting the site.
Both escaped unharmed.
There was no immediate claim of responsibility for the attacks, which is the first of its kind since the city, 150 km north of Baghdad, was retaken from DAESH in April 2015.
One of the attackers 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 attackers continued about to the entrance of the city before detonating the explosives in their pickup truck, killing eight people and wounding 23, the sources said.