Pakistan's police filed terrorism charges against Imran Khan on Monday as the former prime minister held mass rallies seeking a return to office.
The charges followed a speech Mr Khan gave in Islamabad on Saturday, in which he vowed to sue police officers and a female judge, and claimed a close aide was tortured after his arrest, AP reported.
Mr Khan did not immediately address the charges against him.
Mr Khan also accused the government of temporarily blocking YouTube to stop people watching live footage of his speech at a political rally, Reuters reported.
He has made speeches to gatherings across the South Asian nation as he pushes for new elections after being ousted from power in April through a parliamentary vote.
The YouTube blocking accusation followed a ban on Saturday by the electronic media regulator on the live broadcast of Mr Khan's speeches, referring to what it called his "hate speech" against state institutions.
Pakistan’s opposition Tehreek-e-Insaf party, Mr Khan’s political party, had published videos online showing supporters surrounding his home to potentially stop police from reaching it.
Hundreds remained there early on Monday, AP reported.
Under Pakistan’s legal system, police file what is known as a first information report, detailing the charges against an accused, to a magistrate judge who allows the investigation to move forward.
Typically, police then arrest and question the accused.
The report against Mr Khan includes a testimony from Magistrate Judge Ali Javed, who described being at the Islamabad rally and hearing Mr Khan criticise the inspector general of Pakistan’s police and another judge.
“You also get ready for it, we will also take action against you. All of you must be ashamed," Mr Khan said.
Mr Khan could face several years in prison because of the new charges. He is accused of threatening police officers and the judge.
But he has not been detained on other lesser charges levied against him in his recent campaigning against the government.
In a statement, the PTI said the latest accusations against Mr Khan were "frivolous".
"We have serious reservations on this politically motivated move which leads towards further instability in the country," it said.
Meanwhile, the hundreds of supporters, gathered outside Mr Khan's hilltop mansion in the capital, vowed to prevent his arrest on anti-terrorism accusations, Reuters cited officials of his political party as saying.
They chanted slogans against the government of Prime Minister Shehbaz Sharif, which took over after Mr Khan's ouster.
"If Imran Khan is arrested ... we will take over Islamabad with people's power," a former minister in his cabinet, Ali Amin Gandapur, threatened on Twitter, as some party leaders urged supporters to prepare for mass mobilisation.
Another former ministerial colleague, Murad Saeed, told local television channels that the police had issued orders for Mr Khan's arrest.
Mr Khan's aide, Fawad Chaudhry, told reporters outside an Islamabad court that the party had applied for bail for the leader ahead of any arrest.
The use of anti-terrorism laws as the basis of cases against political leaders is not uncommon in Pakistan, where Mr Khan's government also used them against opponents and critics.
The opposition leaders warned Monday that authorities would cross a "red line" if they arrested Mr Khan, AFP reported.
"Wherever you are, reach Bani Gala today and show solidarity with Imran Khan," tweeted former information minister Fawad Chaudhry, referring to Khan's home. "Imran Khan is our red line."
