The majority of Khan's supporters were set free from Punjab province jails on orders from Chief Minister Shahbaz Sharif, his spokesman Rana Arshad said.
Shah Mahmood Qureshi, a senior opposition leader, alleged that the government was still holding some senior aides and was mistreating some of the detainees. "We want them treated well," he said.
Khan's party had threatened to lock down the capital today to force Prime Minister Nawaz Sharif to resign over a financial scandal. Authorities banned all protests in Islamabad in response, and the arrests followed several days of clashes in which police used tear gas and batons against stone-throwing Khan supporters.
Sharif has been under immense pressure from the opposition to step down after his family members were named in leaked financial documents from Panamanian law firm Mossack Fonseca. He has repeatedly denied that either he or his relatives were involved in corruption and has offered to comply with any inquiries or investigations.
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Lawyers for both the opposition and the government will appear before the court tomorrow to discuss the possibility of forming an independent commission to investigate the issue.
Thousands of Khan's supporters gathered today at a park in Islamabad, singing and dancing, and waiting for Khan's arrival.