ISLAMABAD: Hundreds of supporters of Pakistan's former prime minister, Imran Khan, gathered on Monday outside his hilltop mansion in the capital, Islamabad, vowing to prevent his arrest on anti-terrorism accusations, officials of his political party said.

The move follows a police case filed against Khan on Saturday for threatening government officials in a public speech about the alleged police torture of one of his aides, who faces sedition charges for inciting mutiny in the powerful military. 

The protesters chanted slogans against the government of Prime Minister Shehbaz Sharif, which took over after Khan's ouster in a confidence vote in April.

"If Imran Khan is arrested ... we will take over Islamabad," a former minister in his cabinet, Ali Amin Gandapur, said on Twitter, as some party leaders urged supporters to prepare for mass mobilisation.

Another former ministerial colleague, Murad Saeed, told domestic television channels that the police had issued orders for Khan's arrest.

Islamabad police declined to confirm this, however.

The use of anti-terrorism laws as the basis of cases against political leaders is not uncommon in Pakistan, where Khan's government also used them against opponents and critics.

Saturday's police report, seen by Reuters, cited Khan's comments that he "would not spare" Islamabad's police chief and a female judge for the arrest of his aide.

"The purpose of the speech was to spread terror amongst the police and the judiciary and prevent them from doing their duty," police said in the report.

Legal experts say the public threats put the officials' lives at stake, and actually amounted to threatening the state, so that the anti-terrorism charges apply.

The military has also become a target for Khan, who has said it did not help him ward off a U.S. conspiracy that toppled him, a charge Washington has denied.

The military, which has ruled directly for over three decades of Pakistan's 75-year history, has rebuffed Khan's claim. It also denies meddling in politics.

Pakistan's electronic media regulator has banned the live transmission of Khan's speeches as being inflammatory.