Police operation began just after midnight and officers were still raiding the houses of supporters late in the day, says Fawad Chaudhry, a spokesperson for Khan's Tehreek-e-Insaf party.
The key opposition party led by recently ousted PM Imran Khan has accused police of detaining dozens of its supporters in an attempt to foil a planned protest seeking to force Pakistan's government into calling early elections.
Fawad Chaudhry, a spokesperson for Khan's Tehreek-e-Insaf party, said late on Monday the police operation began just after midnight and officers were still raiding the houses of supporters late in the day.
Khan took to Twitter, condemning the arrests of his supporters.
No government official was immediately available for comment.
The development came two days after Khan urged his supporters to gather in Islamabad on Wednesday for a demonstration that he said would continue until the government announced a date for snap elections.
Peaceful protest is the right of all our citizens. The brutal crackdown on PTI ldrs & workers in Punjab & Islamabad has once again shown us what we are familiar with - the fascist nature of PMLN when in power. The present crackdown also raises serious questions abt the Handlers.— Imran Khan (@ImranKhanPTI) May 23, 2022
Khan accuses US in interview
Khan, who served as prime minister for over three and half years, was ousted by a no-confidence vote in parliament in April. He was replaced as prime minister by Shehbaz Sharif.
Khan contends his removal was the result of a US-organised plot. Washington has denied the claim, and Sharif calls it a pack of lies.
In an interview with CNN on Monday, Khan repeated his claims, accusing US Assistant Secretary of State for Central and South Asia Donald Lu of orchestrating Khan's ouster.
Khan said Lu had threatened Pakistan's ex-envoy to the US, Asad Majeed, of "consequences" if Khan was not removed in a no-trust vote.
"Imagine telling the ambassador of a country of 220 million people that you get rid of your prime minister," Khan said.