At least three Pakistani police officers were shot dead and 70 more wounded when supporters of a banned Islamist party opened fire at a rally near Lahore on Wednesday, the country’s interior minister has said.

The outlawed party Tehreek-e-Labbaik Pakistan (TLP) has 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.

The group is protesting over the detention of its leader, Saad Rizvi, who was arrested in April after the TLP was outlawed, and demanding the expulsion of the French ambassador.

“They opened fire on police with Kalashnikovs … Three policemen were martyred,” the interior minister, Sheikh Rasheed Ahmad, told a press conference, adding that eight of those injured were in a critical condition.

The Punjab police chief, Rao Sardar Ali Khan, said in a separate press conference that four officers had died on Wednesday.

The TLP in turn accused the police of firing on the crowd, and said four of its supporters had been killed.

Police in Punjab province, of which Lahore is the capital, have denied using guns or rubber bullets and would not comment on claims that protesters had been killed.

“We have used no such weapons against them,” a police spokesperson said.

The latest demonstration began on Friday in Lahore, which is the group’s stronghold city, with thousands of people marching northwards towards the capital, Islamabad.

Clashes between the two sides in Lahore on Friday left two police officers dead, while the TLP reported on Saturday that five of its supporters had died.

The information minister, Fawad Chaudhry, said on Wednesday that the prime minister, Imran Khan, and the security services had agreed to treat the TLP as a militant group.

Police have closed off major roads and junctions leading to Islamabad, which is about 180 miles from the current protest site.

The government had earlier this week announced a breakthrough in talks with the TLP, but the march resumed on Wednesday.

“We tried our best for the success of the talks but the government is not serious about fulfilling its commitments,” a TLP spokesperson said. “The expulsion of the French ambassador is our main demand.”

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

The TLP has waged an anti-France campaign since the French president, Emmanuel Macron, defended the right of a satirical magazine to republish cartoons depicting the prophet Muhammad – an act deemed blasphemous by many Muslims.

Six police officers were killed in the protests in Islamabad and the neighbouring garrison city of Rawalpindi.

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.