Three Pakistani police were killed in clashes on Friday with demonstrators from a banned Islamist group who rallied to demand the release of their leader and the expulsion of the French ambassador over cartoons depicting the Prophet Mohammed.

The officers were hit by a vehicle which drove at police as thousands of activists from the Tehrik-e-Labaik Pakistan (TLP) movement gathered in the eastern city of Lahore for a march on the capital Islamabad.

Police fired teargas after TLP supporters attacked a security checkpoint, during clashes across the city, police spokesman Arif Rana said.

"They had assured us that they would remain peaceful but they turned violent," he said.