Thousands more protesters massed in Pakistan's major cities Sunday after attempts to disperse an Islamist rally in Islamabad ended in deadly violence, with the military hesitant to respond to a government appeal for help.

An estimated 5,000 demonstrators were occupying roads between Islamabad and neighbouring Rawalpindi, AFP reporters saw, more than twice the number that were in the streets when police and paramilitaries began a bungled operation to clear them one day earlier.

At least 4,750 were in Pakistan's biggest city Karachi, according to traffic officials, up from roughly 200 the day before. In the cultural capital Lahore an estimated 3,400 were occupying main roads.

Reports said the protests had also spread to other cities and towns across the country.

The numbers are still relatively small by Pakistani standards but have grown swiftly. The situation has become more charged since authorities moved to clear the roughly 2,000 people who have blocked a major highway in Islamabad since November 6, paralysing the capital for weeks.

They were met with stubborn resistance by protesters who torched vehicles and threw stones, with at least seven people were killed and dozens injured before security forces retreated on Saturday.

An interior ministry order said the federal government had authorised the deployment of troops to secure the capital until further notice.

But one day after the order was released there was no official military response and no sign of armoured vehicles or soldiers on the streets. A military spokesman declined repeated requests for comment.

Late Sunday an interior ministry official told AFP the paramilitary Rangers force had been empowered to "deal with the protests", but offered no further details.

Civil-military relations have long been fraught in Pakistan, with the military ruling the country for nearly half of its 70-year history.

The little-known Islamist group at the centre of the protests, Tehreek-i-Labaik Ya Rasool Allah Pakistan (TLY), is demanding the resignation of Pakistan's law minister Zahid Hamid over a hastily-abandoned amendment to the oath, which election candidates must swear.

Demonstrators have linked the issue to blasphemy -- a highly contentious matter in Muslim Pakistan that has fuelled violence many times before.

TLY leader Khadim Hussain Rizvi repeated the demand in a press conference Sunday and insisted terrorism charges be levelled against top officials including former prime minister Nawaz Sharif and current leader Shahid Khaqan Abbasi.

He called for a general strike across the country Monday, and declared that TLY will "fully participate" in general elections due to be held next year.

Rizvi said his group was "negotiating" but refused to offer further details, including of who with, and vowed the sit-in would continue "at any cost".

"We are not scared of these bullets. We have to die one day so why not die for the honour of the holy Prophet," he said.

- Broken teeth -

Earlier, at a main stage set up at the centre of the sit-in, demonstrators were playing religious songs as more groups arrived. A military helicopter flew briefly overhead but otherwise few members of the security forces were in sight.

"I don't care if my wife and child ... die of hunger, for me nothing matters more than the honour of my Prophet," Riaz Shah, a labourer from Lahore who has been at the sit-in since it began, told AFP.

He dismissed fears of military intervention, saying the army "would not come here and dishonour the Prophet".

Pakistan's media authority lifted a ban on television broadcasts and authorities said social media sites were no longer being restricted, after an information blackout earlier in the day sparked confusion about the state of the protests.

But many schools announced closures and commuters braced for another week of traffic chaos.

"People's businesses have been destroyed, people are unable to go on their jobs, to hospitals, they are not sending their children to schools," said resident Maqbool Ahmed, calling for the army to "disperse them up by beating them with clubs".

The violence is the latest blow to the embattled Pakistan Muslim League (Nawaz) government ahead of the 2018 election, and after its leader Nawaz Sharif was deposed as prime minister over graft allegations this summer.

Analysts said the government had allowed a relatively small protest by an obscure group to grow into a potentially dangerous situation.

The government's predicament was "daunting", analyst Michael Kugelman of the Wilson Center in Washington told AFP, adding that its ability to survive "depends on the trajectory of the protests".