Pakistani police arrested several lawmakers on Sunday as thousands of opposition protesters marched on the capital, seeking the release of the country's jailed former Prime Minister Imran Khan.

The lawmakers, including the chief whip of the main opposition, Pakistan Tehreek-e-Insaf (PTI) were arrested while on their way to the capital Islamabad from different districts of northeastern Punjab province, the party and police confirmed.

Thousands of PTI supporters gathered at the border of Punjab and northwestern Khyber Pakhtunkhwa border to start marching toward the heavily fortified capital.

The PTI governs Khyber Pakhtunkhwa, which borders neighboring Afghanistan.

Former President Arif Alvi also joined the protesters in the Khyber Phaktunkhwa's capital Peshawar to proceed towards Islamabad, the party announced in a video post on X.

Footage aired on local broadcaster Geo News showed Khyber Pakhtunkhwa Chief Minister Ali Amin Gandapur surrounded by a group of lawmakers and supporters, making a prayer before leading the march.

The channel, citing party sources, claimed that Khan's wife, Bushra Bibi, who had not been scheduled to attend the protest, also joined the march.

Bibi was recently granted bail by an Islamabad court in a graft case.

Internet services were suspended and all major roads leading to Islamabad were blocked.

Police placed containers at entry and exit points of Islamabad, Lahore, Rawalpindi, and other cities, mainly at the borders of northwestern Khyber Pakhtunkhwa (KP) province, which is governed by Khan's Pakistan Tehreek-e-Insaf (PTI) party, to hold off protesters.

The PTI has given a "final march" call to stage a sit-in near parliament until Khan is released.

Footage by broadcasters showed giant containers placed on different sections of roads in Islamabad as police arrested more than 500 PTI activists from across the country, mainly from adjoining northeastern Punjab province.

The government warned that protesters will be dealt with "iron hands" as thousands of police and paramilitary troops have been deployed to foil the protest.

Interior Minister Mohsin Naqavi told reporters that "preparations" have been finalized to foil the opposition's "unlawful" march.

KP Chief Minister Ali Amin Gandapur said party workers would reach the D-roundabout near parliament "come what may," and would only leave the capital when Khan is released.

On Friday, the Islamabad High Court, in a petition from Islamabad's traders, directed the government to take necessary measures to maintain law and order in the capital, particularly as the Belarusian president is scheduled to arrive during the weekend.

Khan, 72, has been languishing in a jail in the northeastern garrison city of Rawalpindi since August 2023.

The former cricket star is facing a string of cases, ranging from corruption to terrorism. He said the cases are a sham.