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.
Imran Khan has been in jail for over a year. (AP PHOTO)
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.
Khan, who has been in jail for over a year and faces more than 150 criminal cases, remains popular. PTI says the cases are politically motivated.
Authorities say only courts can order the release of Khan, who was ousted in 2022 through a no-confidence vote in Parliament. He has been imprisoned since his first conviction in a graft case, in August 2023, and has been sentenced in several cases.
with AP
