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.

TLP media coordinator Saddam Bukhari said police attacked a peaceful rally but Punjab Chief Minister Usman Buzdar, who confirmed the deaths of the officers, condemned the demonstrators. "No one can be allowed to take the law into their own hands," he said.

The protests, over a series of caricatures published in the French satirical magazine Charlie Hebdo last year, follow serious clashes in April in which at least five police and three activists were killed and hundreds wounded.

Following the April clashes in which TLP activists blocked highways, railways and access routes to cities and battled police, the authorities arrested their leader, Saad Hussain Rizvi and banned the group.

Rizvi has been in detention since his arrest and the government has designated TLP as a terrorist movement.

Authorities had been trying to negotiate with the group, which rallied its supporters outside its Lahore headquarters for the last two days, but the negotiations broke down and the group called on supporters from around Pakistan to converge on the capital Islamabad.

The main arteries to and from Lahore and Islamabad were blocked with shipping containers to prevent demonstrators entering the city. The diplomatic enclave in Islamabad, where most foreign embassies are located, was also blocked off.

Nearly 1,000 police were injured in the April clashes, which were halted only after government announced a parliamentary vote on expelling the French ambassador over the publication of caricatures of the Prophet Mohammad by the Paris-based satirical magazine Charlie Hebdo.

The magazine first published the cartoons in 2006, outraging millions of Muslims who considered them deeply insulting. It republished them last year to mark the opening of a trial over a deadly attack on the magazine by Islamist militants in 2015.