Already, angry protesters stormed a radio station in the northwest on Wednesday, and supporters clashed with police in the capital of Islamabad.
The 70-year-old politician was ousted in a no-confidence vote last year but remains the country’s most popular opposition figure.
His dramatic arrest — when he was pulled out of a hearing on one set of charges to be arrested on another set — was the latest confrontation to roil Pakistan.
He is the seventh former prime minister to be arrested in the country, which has also seen interventions by its powerful military over the years.
The move comes at a time when the cash-strapped nation is trying to avoid a default.
Khan has denounced the cases against him, which include corruption and terrorism charges, as a politically motivated plot by his successor, Prime Minister Shahbaz Sharif, to keep him from returning to power in the next elections which are to be held later this year.
Khan has campaigned against Sharif and demanded early elections.
Khan’s Pakistan Tehreek-e-Insaf party appealed for calm, but the standoff put the country on high alert after Tuesday’s clashes.
Police deployed in force across the country, and placed shipping containers on a road leading to the sprawling police compound in Islamabad where Khan is being held.
In Peshawar, supporters raided a building housing Radio Pakistan, damaging equipment and setting fire to it, said police official Naeem Khan.
Some of the employees were trapped inside, he said, and police were trying to restore order.
Meanwhile, in eastern Punjab province, the local government asked the army to step in after authorities said 157 police officers were injured in clashes with Khan supporters.
Police arrested 945 Khan supporters in eastern Punjab province alone since Tuesday — including Asad Umar and Shah Mahmood Qureshi, two senior leaders from Khan’s party.
Amid heightened security, Khan appeared before a judge at a temporary court inside a police compound on Wednesday.
Pakistan’s GEO television broadcast footage showing him seated in a chair, holding documents. He appeared calm but tired.
In the latest case, Khan has been accused of accepting millions of dollars worth of property in exchange for providing benefits to a property tycoon.
The National Accountability Bureau, which is investigating, asked to hold him for 14 days, but the tribunal granted eight days.
Khan’s legal team has challenged the arrest in an Islamabad court and is considering doing the same at the country’s Supreme Court.
The National Accountability Bureau has detained and investigated former officials, including former prime ministers, politicians and retired military officers.
But some view the bureau as a tool used by those in power, especially the military, to crack down on political opponents.
When Khan was in power, his government arrested Shahbaz Sharif, then the opposition leader, through the bureau.
Sharif was facing multiple corruption cases when he managed to oust Khan. The charges were later dropped for lack of evidence.
When he was detained on Tuesday, Khan was appearing in court on multiple graft charges brought by Islamabad police.
As he showed up in court, dozens of agents from the accountability bureau backed by paramilitary troops stormed the courtroom, breaking windows after Khan’s guards refused to open the door.
Mobs angered by the dramatic arrest set fire to the residence of a top army general in the eastern city of Lahore, and supporters attacked the military’s headquarters in the garrison city of Rawalpindi near the capital, Islamabad.
They did not reach the main building housing the offices of army chief General Asim Munir.
Other demonstrators tried to reach the prime minister’s residence in Lahore, but were driven off by baton-wielding in police. Still more attacked vehicles carrying troops and hit armed soldiers with sticks. So far, police and soldiers have not fired at protesters.
The military has not commented on the attacks on its facilities. None of the leaders from Khan’s party denounced the attacks on the military, though they have appealed to their supporters to be peaceful.
By morning, police said some ,000 protesters still surrounded the fire-damaged residence in Lahore of Lieutenant General Salman Fayyaz Ghani, a top regional commander.
They chanted slogans at the military, including “Khan is our red line and you have crossed it”.
Ghani and his family members were moved to a safer place when the mob on Tuesday first attacked their sprawling house.
Khan was finally indicted on Wednesday in the original graft case and pleaded not guilty.
Amid violence, Pakistan’s telecommunication authority blocked social media, including Twitter. The government also suspended internet service in Islamabad and other cities.
Classes at some private schools were cancelled on Wednesday, and several social media sites remained suspended, depriving millions of people of access.
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Rights group Amnesty International said it was alarmed by reports of Pakistani authorities blocking access to mobile internet networks and social media.
Amnesty urged authorities to show restraint, saying clashes between law enforcement and Khan’s supporters risk human rights violations.