Pakistani police arrested thousands of Imran Khan supporters as the capital remained under lockdown ahead of a rally there to demand the ex-premier’s release from prison, a security officer said Sunday.

Khan has been behind bars for more than a year and has over 150 criminal cases against him. But he remains popular and his political party, Pakistan Tehreek-e-Insaf or PTI, says the cases are politically motivated.

Shahid Nawaz, a security officer in eastern Punjab province, said police have arrested more than 4,000 Khan supporters. They include five parliamentarians.

Pakistan has since Saturday sealed off Islamabad with shipping containers and shut down major roads and highways connecting the city with PTI strongholds in Punjab and northwestern Khyber Pakhtunkhwa provinces.

Tit-for-tat teargas shelling between the police and the PTI was reported on the highway bordering Punjab and Khyber Pakhtunkhwa.

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

The government and Interior Ministry posted the announcement on the social media platform X, which is banned in Pakistan. They did not specify the areas, nor did they say how long the suspension would be in place.

“Internet and mobile services will continue to operate as usual in the rest of the country,” the posts said.

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

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

PTI spokesperson Sheikh Waqas Akram said Khan's wife Bushra Bibi was traveling to Islamabad in a convoy led by the chief minister of Khyber Pakhtunkhwa, Ali Amin Gandapur.

“She cannot leave the party workers on their own,” said Akram.

There was a festive mood in Peshawar, with PTI members dancing, drumming and holding up pictures of Khan as cars set off for Islamabad.

The government is imposing social media platform bans and targeting VPN services, according to internet advocacy group Netblocks. On Sunday, the group said live metrics showed problems with WhatsApp that were affecting media sharing on the app.

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

Last month, authorities suspended the cellphone service in Islamabad and Rawalpindi to thwart a pro-Khan rally. The shutdown disrupted communications and affected everyday services such as banking, ride-hailing and food delivery.

The latest crackdown comes on the eve of a visit by Belarusian President Alexander Lukashenko.

Interior Minister Mohsin Naqvi said authorities have sealed off Islamabad's Red Zone, which houses key government buildings and is the destination for Khan's supporters.

“Anyone reaching it will be arrested,” Naqvi told a press conference.

He said the security measures were in place to protect residents and property, blaming the PTI for inconveniencing people and businesses.

He added that protesters were planning to take the same route as the Belarusian delegation, but that the government had headed off this scenario.

Naqvi denied cellphone services were suspended and said only mobile data was affected.