Khan has been demanding early elections and claiming his removal from office was the result of a US-organised plot.
Pakistan has banned ousted Prime Minister Imran Khan from holding a massive, planned rally in the capital of Islamabad.
The ban came after police detained hundreds of supporters of ousted Khan overnight ahead of a major sit-in planned by the former leader, senior party members and police sources said on Tuesday.
The government has pledged to block the protest.
According to Fawad Chaudhry, a spokesman for the Tehreek-e-Insaf party, police raids against their supporters started shortly after midnight Monday.
Homes were still being raided on Tuesday morning and at least 400 supporters of the party were arrested across the country, Chaudhry said.
Authorities confirmed the raids but refused to share details about any arrests.
Khan condemned the arrests on Twitter.
PPP, PMLN and JUI Marches against our govt were never stopped nor did we carry out any crackdown on their workers. This is the difference between democrats and kleptocrats.— Imran Khan (@ImranKhanPTI) May 23, 2022
March on Islamabad
Khan, a cricket star turned populist politician, was kicked out of power last month in a vote of no-confidence, but has since pressured the country's fragile new coalition government by staging mass rallies across the country.
Khan has claimed his removal was the result of a US-organised plot.
Khan plans on Wednesday to lead tens of thousands of supporters from his power base in the northwestern city of Peshawar to the capital Islamabad demanding fresh elections.
Interior Minister Rana Sanaullah warned Khan that he would “not be allowed to disrupt peace in Islamabad" and would be arrested if needed, should the rally go ahead.
Sanaullah said the decision to ban the rally was taken after Khan’s Tehreek-e-Insaf party failed to assure the administration in writing that the rally would be peaceful.
Everybody has the right of freedom of expression and peaceful protest; however, the PTI did not want a peaceful protest. If they hadn’t called it a “bloody march”, the government wouldn’t have stopped them. (1/2)— Rana SanaUllah Khan (@RanaSanaullahPK) May 24, 2022
Earlier Tuesday, authorities stepped up security in Islamabad, deploying additional officers and paramilitary Rangers.
Large shipping containers were placed on a key road leading to the parliament building, to prevent Khan’s supporters from getting close and possibly staging a sit-in there.