Four Pakistani security troops were killed on Tuesday in the capital, Islamabad, run over by a convoy of protesters seeking the release of jailed former Prime Minister Imran Khan, the prime minister’s office said.

Thousands of Khan’s supporters marched on the capital, breaking through barricades in response to his call for a sit-in protest near parliament to press demands ranging from their leader’s release to the government’s resignation.

“It is not a peaceful protest. It is extremism,” Prime Minister Shehbaz Sharif said in a statement issued by his office, condemning the bloodshed as being aimed at achieving “evil political designs”.

Some vehicles in a convoy of protesters ran over security officers, killing the paramilitary officers, it added.

The interior ministry attributed the attacks to “miscreants” but did not identify them further, saying four troops were killed.

Khan’s Pakistan Tehreek-e-Insaaf (PTI) did not immediately respond to a request for comment on the government’s accusations.

Khan’s wife, Bushra Bibi, and a key aide, Ali Amin Gandapur, who is the chief minister of Khyber Pakhtunkhwa province, led a march that wended its way into the capital early on Tuesday, his party and Reuters witnesses said.

Khan has told marchers to head for a roundabout just outside parliament. His party's demands include a rollback of constitutional amendments it says the government made to curtail the powers of the judiciary.