Over 80 police personnel have been injured in clashes with supporters of jailed former Prime Minister Imran Khan taking part in a march near Islamabad, Interior Minister Mohsin Naqvi said on Saturday.
The march, which is being led by the head of the northwestern province of Khyber-Pakhtunkhwa, where Khan's party remains in power, aims to gather in the capital, defying a ban on congregations, to press for Khan's release and agitate against the ruling coalition.
"The convoy, led by the chief minister, fired on the police and continuously used teargas against law-enforcers," Naqvi told journalists.
He said more than 80 police officers had been treated for injuries since Friday, when clashes broke out just outside the city during an anti-government rally.
Authorities have sealed off Islamabad and blocked cellphone services to prevent the gathering.
Islamabad is on high alert ahead of a series of top-level diplomatic events scheduled over the next two weeks, including a visit by India's Foreign Minister Subrahmanyam Jaishankar.
Naqvi said while the convoy was heavily armed, the police had been instructed not to carry weapons to prevent the situation from escalating. The government has deployed the army to enhance security in Islamabad.
The protesters plan to gather in the city's red zone, which houses the country's parliament and a fortified enclave of foreign embassies.
Khan's Pakistan Tehreek-e-Insaf (PTI) party denies using violence, and says it wants to hold a peaceful gathering.
Naqvi had previously called on the PTI to delay any gathering until after diplomatic engagements in the city, including a Shanghai Cooperation Organisation (SCO) meeting on October 15-16 which will be attended by delegations, including from China, Russia and India.
On Saturday, Naqvi said the authorities had intelligence that the protesters planned to disrupt the SCO conference in a bid to gain attention.
"We can't allow this. I will say to them again, to not cross more red lines - don't make us take extreme steps," Naqvi said.
The PTI, which says the Islamabad protest is just for one day, is also holding a gathering in the eastern city of Lahore on Saturday, where a lockdown of roads is in place.