Supporters of a Pakistani radical Islamist party 'Jamiat Ulema-e-Islam' participate in an anti-government march, in Islamabad, Pakistan, Friday, Nov. 1, 2019

The protest caravan rolled into Islamabad on Thursday led by firebrand cleric Maulana Fazlur Rehman, who heads the Jamiat Ulema-e-Islam party

ISLAMABAD: Tens of thousands of Islamists remained in a protest camp in the heart of Pakistan's capital on Saturday amid tight security, as authorities deployed additional shipping containers and riot police to block access to key government buildings.

The protest caravan rolled into Islamabad on Thursday led by firebrand cleric Maulana Fazlur Rehman, who heads the Jamiat Ulema-e-Islam party. He's given Prime Minister Imran Khan until Sunday night to resign over the country's economic hardships.

Khan says he won't succumb to pressure.

Rehman has hinted he may try to force Khan to step down by staging a mass march on the "Red Zone," where parliament, the prime minister's residence, government offices and foreign embassies are located.

Authorities in Islamabad were seen early Saturday moving more rows of massive shipping containers onto roads leading to the Red Zone. Paramilitary forces were also deployed. Authorities in Islamabad were seen early on Saturday moving more rows of massive shipping containers onto roads leading to the Red Zone.

"This mammoth crowd has the capacity to arrest the prime minister themselves from the prime minister's house if he has not resigned within two days," Rehman said Friday night, while asking Pakistan's powerful military not to side with Khan.

Rehman had initially denied female journalists access to his all-male encampment, which stretches over a kilometre (mile) along a highway and into an open area allocated by the government. His ban caused a storm on social media, and women reporters were eventually allowed into the camp.

The hard-line cleric has campaigned for regressive legislation targeting women, and opposed legislation to eliminate of violence against women. He has also refused to allow women members of his party to participate in the march.

Rehman has been accusing the military of influencing the 2018 parliamentary elections that saw Khan's Pakistan's Tehreek-e-Insaf party come into power. Rehman's seven-party political alliance, Muttahida Majlis-e-Amal, could secure only 16 seats in the 342-member National Assembly, the lower house of parliament. Khan received 155.

Rehman, without naming the army, said Friday that: "If it is felt that state institutions were behind the rigged elections and protecting these incompetent and illegitimate rulers, we won't be able to stop ourselves from forming an opinion about these institutions."

For his part, Khan told a gathering Friday in the northern city of Gilgit that he "will continue to hold the corrupt accountable," and that he's not afraid of Rehman's threats to his government. He met Saturday with his cabinet and party leaders to discuss how to tackle the situation.

The mass rally comes after Pakistani businesses observed a nationwide strike earlier this week against recently enacted taxes, which the opposition says were imposed as part of the International Monetary Fund's $6 billion bailout package for Pakistan.

Also Friday, military spokesman Maj. Gen Asif Ghafoor told a local television station that "Chaos is not in the interest of the country ... all democratic issues should be dealt with in a democratic manner." He said the opposition should understand that the army is impartial and supports the democratically elected government, not political parties.