Pakistani police fired teargas, baton-charged and detained supporters of ousted Prime Minister Imran Khan on Wednesday to stop them from reaching the capital Islamabad to demand fresh elections, officials and witnesses said.
Clashes between Khan's supporters and police were reported in multiple cities.
Khan, ousted in a confidence vote last month after losing his partners in his coalition, has urged supporters to march on Islamabad and stay there until the new government is dissolved and a date for a fresh election is announced.
Islamabad's entry and exit routes have been blocked, as well as important civic sites, officials said. Entry and exit points were also blocked to and from all major cities in Punjab province and on the Grand Trunk Road (GTR).
"No blockade can stop us," Khan said from atop a truck on the GT road on his way to Islamabad from the northwestern city of Peshawar.
"We will remain in Islamabad till the announcement of dates for dissolution of assemblies & elections are given," he later tweeted.
The government has said Khan's march is illegal and accuses him of seeking to bring protesters to Islamabad with "evil intentions".
Khan's supporters also clashed with security forces in other major cities, including the southern port city of Karachi and the eastern city of Lahore.
A mob torched a prison van in Karachi after clashing with police, and another group of protesters set fire to several trees along a main thoroughfare in Islamabad, officials said.
The political violence has compounded uncertainty in the nuclear-armed South Asian nation ahead of a likely announcement by the International Monetary Fund (IMF) later in the day on whether it will resume a $6 billion rescue package.
With falling foreign reserves, a fast-crashing rupee, and double-digit inflation, Pakistan's new government is struggling to stop a downward economic spiral.
Live local TV footage showed police fighting with Khan's supporters, beating them and in some places breaking their vehicles' windscreens and bundling them into police vans.
Amjad Malik, an interior ministry official, told Reuters no one had been seriously injured in the clashes.
Interior Minister Rana Sanaullah later said police had carried out a total of 4,417 swoops on Khan supporters' homes, offices and on protest rallies and had arrested nearly 1,700 people. Of those, 250 were later freed, he said.
Khan has promised to rally more than two million people in Islamabad.
"We haven't stopped anyone from exercising their constitutional and legal right to hold a rally or take part in democratic politics, but we can't allow anyone to sow violence and chaos," said Sanaullah.
Pakistan's Supreme Court, later in the day, ordered the government and Khan's party to negotiate on holding a peaceful public meeting in Islamabad.
Prime Minister Shehbaz Sharif said his government was trying to clear up an economic mess that he blamed Khan for.
"You've handed over a sinking economy to us, and now you're planning sit-ins and protest," Sharif said in Islamabad. "We are trying to energize this weak economy."