Imran Khan, Pakistan's imprisoned ex-prime minister, called on more followers to join rallies against his detention in the capital late Tuesday, following a day of fatal clashes between demonstrators and police forces.

Since Sunday, convoys of pro-Khan protesters have been advancing through Islamabad, removing barriers and engaging police and paramilitary troops with rubber bullets and tear gas and prompting a lockdown.

Since the February election, his Pakistan Tehreek-e-Insaf (PTI) party has resisted a government crackdown with frequent demonstrations, but Tuesday's is by far the largest to hit the city.

The demonstrations come in response to Khan's call for his supporters to march on the capital, demanding his release and free elections.

Khan has been in jail for over a year, facing numerous charges that he claims are politically motivated.

His supporters allege widespread rigging in February's elections and accuse the ruling coalition, led by Prime Minister Shehbaz Sharif, of orchestrating his imprisonment to prevent his return to power.

Khan delivered a message from his detention cell outside Islamabad, urging more people to join protesters seeking to take a public area in the city's administrative enclave. 

"Those who haven't yet joined the protest must also head to D-Chowk [square], "Khan said in a message posted by his party on social media.

Pakistani Army deployed in Islamabad, given shoot-on-sight orders

Following the protests, the federal government deployed the army in the national capital along with shoot-at-sight orders on Tuesday, state-run media said.

Four paramilitary personnel and two policemen have been killed and over 100 security personnel injured.

Despite a prohibition on public meetings, AFP journalists reported seeing over 10,000 demonstrators clashing with police in the city center. 

"This is not our government, this government is made up of traitors," demonstrator Abdul Rashid told AFP, adding  "Long live Imran Khan."

"These disruptive elements do not seek revolution, but bloodshed," Prime Minister Shehbaz Sharif stated. "This is not a peaceful protest, it is extremism." 

PTI legislator Waqas Akram told AFP, "They treat their own people as enemies," accusing the state response as being unjustified and unreasonable.

The authorities accused demonstrators of seeking to delay Belarusian President Alexander Lukashenko's three-day state visit, which began on Monday. "There will be no negotiations with violent people," Interior Minister Mohsin Naqvi stated to reporters late Tuesday.

Last Monday, the Islamabad municipal government issued a two-month ban on public meetings. However, PTI convoys traveled from their power base in northern Khyber Pakhtunkhwa to the most populated province, Punjab.