ISLAMABAD — Tens of thousands of protesters are closing in on Pakistan's capital Islamabad as part of nationwide protests calling for the release of former prime minister Imran Khan.

Authorities have enforced a security lockdown for the last two days to block the protesters, whom Khan has called on to march on parliament for a sit-in demonstration to demand his release, while highways into the city have been barricaded.

At least one policeman was killed and dozens on both sides wounded as Khan's supporters clashed with security forces outside the capital Islamabad on Monday, according to a Reuters report.

The march is in response to a "final" protest call made by Khan to his supporters, where he also called on them to remain in the capital until the government addresses their demands.

Some top leaders of Khan's Pakistan Tehreek-e-Insaf (PTI) party met him at the Rawalpindi prison where he is serving a three-year jail term for corruption - a charge he denies.

Shahid Nawaz, a security officer in eastern Punjab province, said on Monday that police have already detained more than 4,000 Khan supporters, including five parliamentarians.

In a news conference, Interior Minister Mohsin Naqvi said authorities will arrest more Khan supporters if they reach Islamabad’s Red Zone, which has been sealed off to protect government buildings.

“Anyone reaching it will be arrested,” he said.

Naqvi said the security measures were in place to protect residents and property, blaming Khan’s party for inconveniencing people and businesses.

Earlier on Monday, hundreds of Khan’s supporters started their march to Islamabad, reaching the fringes of the capital, according to officials and his party.

Videos posted on social media showed allies of Khan, rallying the crowd and urging them to march ahead. Convoys of hundreds of cars were also seen.

In Peshawar, supporters of Khan were in a festive mood, with PTI workers dancing, drumming and holding up pictures of their leader as cars set off for Islamabad.

Khan’s wife Bushra Bibi and key aide Ali Amin Gandapur, who is the chief minister of Khyber Pakhtunkhwa province, are leading a rally that arrived just outside Islamabad on Sunday night, PTI said.

Khan has been behind bars for more than a year and is facing more than 150 criminal cases. But he remains popular and his party has described the cases as politically motivated.

Authorities have sealed off Islamabad with shipping containers since Saturday and shut down major roads and highways connecting the city with PTI strongholds in Punjab and northwestern Khyber Pakhtunkhwa provinces to prevent Khan’s supporters from reaching Islamabad.

The protest march, which Khan has described as the “final call”, is one of many his party has been holding to seek his release. The party’s last protests in Islamabad early in October had turned violent.

Earlier, on Sunday, Pakistan suspended mobile and internet services “in areas with security concerns”.

But Naqvi, the interior minister, denied suspending mobile phone services, saying only mobile data was affected.

Meanwhile, telecom company Nayatel sent out emails offering customers “a reliable landline service” as a workaround in the areas suffering suspended mobile phone service.

Khan’s supporters rely heavily on social media to rally support for his release and use messaging platforms like WhatsApp to share information, including details of events.

The government, however, is imposing social media bans and targeting virtual private network (VPN) services, according to internet advocacy group Netblocks.

The United States Embassy in Islamabad issued a security alert for Americans in the capital, encouraging them to avoid large gatherings and warning that even “peaceful gatherings can turn violent”.

Khan was voted out of power by parliament in 2022 after falling out with Pakistan’s powerful military.

The military has an outsized role in politics and it mostly decides who will rule the South Asian nation of 241 million. — Agencies