A radical Islamist party on Saturday said seven of its supporters have died in clashes with authorities in Pakistan's eastern city of Lahore after two police officers were killed in the unrest.

The number of Tehreek-e-Labbaik Pakistan (TLP) protesters swelled by thousands on Saturday evening as supporters of the hardline party began marching towards the capital Islamabad without facing any further resistance from police.

TLP supporters use mobile phone flashlights during their protest march towards Islamabad on Friday TLP supporters use mobile phone flashlights during their protest march towards Islamabad on Friday Photo: AFP / Arif ALI

Scores of the group's supporters had gathered after Friday prayers to demand the release of their detained leader, blocking roads and firing projectiles in deadly clashes with police.

The TLP has previously been behind major anti-France protests that earlier this year led to the embassy issuing a warning for all French citizens to leave the country.

Police had used tear gas to disperse the protesters Police had used tear gas to disperse the protesters Photo: AFP / Arif ALI

"Death toll of Tehreek-e-Labbaik Pakistan supporters rose to seven after two more people succumbed to their injuries caused by police firing," the party tweeted on Saturday.

It had earlier said two of the seven supporters died on Friday.

Tens of thousands of protesters appeared to be moving toward Islamabad in a convoy Tens of thousands of protesters appeared to be moving toward Islamabad in a convoy Photo: AFP / Arif ALI

Police in Lahore would not comment on the claim, but on Friday night said two of its officers had died.

Rana Arif, a Lahore police spokesman told AFP earlier on Saturday that officials were carrying out "a defensive operation against the mob... We are only doing shelling to control the crowd."

On Friday, TLP supporters used mobile phones as flashlights during the late hours of the protest On Friday, TLP supporters used mobile phones as flashlights during the late hours of the protest Photo: AFP / Arif ALI

TLP leader Saad Rizvi was arrested in April when Pakistan's government outlawed the party in response to violent anti-France protests.

Thousands of protesters appeared to be moving toward the capital in a convoy but exact numbers are hard to verify with Police and TLP figures varying wildly.

Police have closed off major roads in Islamabad and Lahore using shipping containers to block the march.

The party has vowed not to end the protests or enter talks with the government until their leader is released.

Interior Minister Sheikh Rashid Ahmad, who had been in Dubai to watch Pakistan compete in the T20 cricket World Cup, returned home on Prime Minister Imran Khan's directive to monitor the situation.

The TLP has waged an anti-France campaign since President Emmanuel Macron defended the right of a satirical magazine to republish cartoons depicting the Prophet Mohammed -- an act deemed blasphemous by many Muslims.

Six police officers were killed in April when the TLP staged days of rallies that shut roads and paralysed Lahore, a sprawling metropolis of over 10 million people.

Few issues are as galvanising in Pakistan as blasphemy, and even the slightest suggestion of an insult to Islam can supercharge protests, incite lynchings, and unite most of the country's warring political parties.