Pakistani security forces are on standby to remove more than 1,000 hardline Islamist protesters from central Islamabad.
The demonstrators are angry at the recent execution of police guard Mumtaz Qadri, who assassinated a politician for advocating blasphemy law reform.
They have pledged to defy the authorities and continue their action.
Pakistan’s interior minister has vowed to clear the high-security zone, which the protesters overran on Sunday.
“We don’t want any violence, but we can’t tolerate it any more,” Interior Minister Chaudhry Nisar Ali Khan told protesters late on Tuesday.
He moved a deadline for them to disperse from Tuesday evening to Wednesday.
Talks have since been going on to try to break the deadlock.
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The protesters have also called for the immediate execution of Asia Bibi, a Christian woman convicted of blasphemy.
Her case was championed by moderate Punjab governor Salman Taseer before he was shot dead by Qadri in 2011. Qadri’s supporters say he is a hero and should be considered a martyr.
Critics say the blasphemy laws, which allow the death penalty to be imposed in some cases, are often misused to oppress religious minorities.
Four days of protests in the capital have once again highlighted Pakistan’s deep divisions over its battle with extremism.
The BBC’s M Ilyas Khan in Islamabad says some 600 troops have been deployed at the government’s request in the Red Zone where government buildings are located, but they have largely taken a back seat.
It is thought by some that a clear message from the powerful army could end the protests more quickly, our correspondent says.
The lack of such a move underlines the on-off civilian-military divide in Pakistani politics, he says.