An anti-terrorism court in Pakistan on Thursday extended the interim bail to ousted prime minister Imran Khan till September 12 in a terrorism case registered against him for threatening police, judiciary and other state institutions during a rally in the capital month.

Judge Raja Jawad Abbas Hassan granted bail to the chief of the Pakistan Tehreek-e-Insaf (PTI) party against a surety bond of Rs 100,000, the Express Tribune newspaper reported.

During a rally in Islamabad last month, 69-year-old 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 Additional District and Sessions Judge Zeba 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 was booked under the Anti-Terrorism Act for threatening police, judiciary and other state institutions at his rally.

The anti-terrorism court on August 25 had granted bail to the PTI chief till September 1 against a surety of Rs 100,000.

Khan last week showed willingness to withdraw his controversial remarks against the female judge but stopped short of tendering an apology.

In a written response sent to the Islamabad High Court, Imran claimed of not being aware at the time of passing the remarks that Chaudhry was a judicial officer as he was under impression that she was an executive magistrate.

"The respondent (Khan) submits with humility that if the words he uttered is regarded as inappropriate, he is willing to take them back," Khan said in his reply submitted in the court.

On Thursday, Khan arrived at the Islamabad ATC amid tight security and the proceedings commenced under Judge Abbas, who ordered the prosecutor to grant the PTI chairman interim bail in the four new charges added to the first information report (FIR) in the case.

The final arguments would be heard in the next hearing on September 12.