Pakistan's ousted prime minister Imran Khan on Friday appeared before a sessions court here to personally apologise to Additional Sessions Judge Zeba Chaudhry, the female judge he had allegedly threatened at a public rally.

During a rally in Islamabad on August 20, Khan had threatened to file cases against top police officials, election commission and political opponents over the treatment meted out to his aide Shahbaz Gill, who was arrested on charges of sedition.

He had also taken exception to Judge Chaudhry, who had approved Gill's two-day physical remand at the request of the Capital Territory Police, and said she should "prepare herself as action would be taken against her''.

Hours after the speech, Khan, 69, was booked under the Anti-Terrorism Act for threatening police, judiciary and other state institutions at his rally.

Khan and his lawyers appeared in Judge Chaudhry's court. However, the Pakistan Tehreek-e-Insaf (PTI) chief was informed by the court reader, Choudhry Yasir Ayaz, and stenographer Farooq that the judicial magistrate was on leave, the Dawn newspaper reported.

Khan then left a message for the judge with Ayaz.

"I have come to apologise to judicial magistrate Zeba Chaudhry," he could be heard saying to the court reader in a video shared by the PTI on Twitter.

"You have to tell Madam Zeba Chaudhry that Imran Khan had visited and wanted to apologise if his words hurt her sentiments," he said. The PTI chief then left the court.