Pakistani authorities issued a final warning to members of an Islamist party blocking a main road into the capital, raising fears of a violent clash.
Hundreds of supporters of the Tehreek-e-Labaik Pakistan party have been blocking the route into Islamabad for nearly 10 days, demanding the minister of law be sacked for what they say is blasphemy.
"You all are being given a last warning," the Islamabad deputy commissioner said in the order.
A court had already ordered the party to end the protest, the order added. "After this final announcement, you all are being warned to end the illegal sit-in immediately."
Tehreek-e-Labaik blames the minister, Zahid Hamid, for changes to an electoral oath that it says amount to blasphemy. The government puts the issue down to a clerical error.
Pakistan's blasphemy law is a lightning rod for Islamists, especially since 2011 when the liberal governor of Punjab province, Salman Taseer, was murdered by a bodyguard for questioning it. The law mandates the death penalty for insulting Islam or the Prophet Mohammad (Pbuh).
A spokesman for the Labaik party, Ejaz Ashrafi, said the group would not comply with the deputy commissioner's ultimatum.
"We're not moving," he told Reuters by phone from the sit-in.
Pakistan's Interior Minister Ahsan Iqbal appealed to the protesters to end the sit-in before a delegation of Chinese investors arrived in Islamabad on Monday, making a last offer to negotiate on their demands.
But he added: "If some group tries to hold the state hostage, that behaviour will not be tolerated."
A government official, Khalid Abbasi, said protesters on the road were carrying rods and sticks. Since they were given the warning, he said, hundreds more party workers had joined the sit-in.
The government has blocked several roads with shipping containers in an effort to corral the protesters, causing hours-long traffic jams in and around the capital.
In 2007, a confrontation between authorities and supporters of radical preachers at an Islamabad mosque led to more than 100 deaths.
"All resources can be used to break this sit-in," the deputy commissioner's warning said.