Pakistan Tehreek-e-Insaf (PTI) leaders and supporters gathered at Bani Gala, the residence of party chairman Imran Khan, after unconfirmed reports of his imminent arrest made the rounds.
Former information minister Fawad Chaudhry said Imran was in "high spirits", according to a tweet posted by PTI.
"He is relaxed," said Fawad in response to a question on whether he had met the party chief.
Imran was booked earlier under Section 7 of the Anti-Terrorism Act (punishment for acts of terrorism) regarding his comments during his Islamabad rally a day ago, Aaj News reported on Sunday.
The first information report (FIR), a copy of which is available with Business Recorder, was registered at Islamabad’s Margalla police station at 10pm on Saturday under the complaint of magistrate Ali Javed.
The text of the PTI Chief’s August 20 speech has also been included in the FIR.
The FIR said that at the PTI’s rally at F-9 park a day ago, Imran had “suddenly started frightening and threatening top police officials and a respected female additional sessions judge” during his address.
During his address, Imran had announced that the PTI will file a case against Islamabad’s Inspector General (IG) Dr Akbar Nasir Khan, deputy inspector general (DIG) and Additional District and Sessions Judge Zeba Chaudhry, who remanded the accused PTI leader Shahbaz Gill.
Imran Khan steps up pressure on ‘neutrals’
Earlier on Sunday, responding to Imran's speech, Interior Minister Rana Sanaullah said that the PTI chief should get ready to face the law as he verbally threatened the IG, DIG, and Magistrate Islamabad.
He added that the PTI head will have to be answerable for threatening the officers.
"Pakistan would turn into a jungle if the law does not take its way," Sanaullah had said.
The interior minister added that they cannot let people challenge the writ of the government because it would fan extremism. The PTI chief, addressing a party rally in Islamabad, said that they would lodge cases against the officers for torturing PTI leader Shahbaz Gill.
Later on Sunday night, as unconfirmed reports made the rounds that Imran might be arrested, PTI made calls to its workers and supporters to start gathering at Bani Gala.
It shared on its Twitter page that workers had started to arrive at the residence of the party chief, in order "to protect him".
Former energy minister, and a key member of PTI, Hammad Azhar said the "plan is to arrest Imran Khan at dawn".
Azhar's tweet follows that of PTI leader Murad Saeed who had earlier stated that orders for Imran Khan's arrest had been issued.
The PTI enjoys massive public support in Pakistan. It also retained its NA-245 seat after unofficial results from 263 polling stations showed its lead by a huge margin in Sunday's by-polls held after the death of PTI lawmaker Aamir Liaquat Hussain.