They detonated the car as officers moved to search it, said police chief Pervaiz Rathor. Two of the seven injured were in critical condition, he said.

“By putting their lives in danger, our men have saved the city from enormous sabotage,” Rathor told reporters at the scene. Witnesses described a terrifying scene of blood and body parts. “I am still trying to come to my senses. It was horrible,” Mohammad Saeed, a police constable who saw the explosion, told Geo TV.

Checkpoints have become a common sight across Pakistan amid a surge in violence. The Lahore blast came hours after a suicide bomber killed 35 people outside a bank in Rawalpindi, near Islamabad.

Footage on television showed at least three vehicles were damaged. Personnel from the bomb disposal squad checked the car that was being used by the bombers to see if there were any more explosives in it. Body parts of the bombers, including a severed head, had been found, he said.

The area was cordoned off and traffic on the busy motorway was stopped.

Suspected militants have struck repeatedly in the past month, killing more than 300 people in apparent retaliation for an army offensive in a Taliban stronghold.