ISLAMABAD (AFP) - Pakistani anti-corruption officials are to appear before the Supreme Court on Thursday over orders to arrest the prime minister and 15 other people on accusations of graft in 2010.

The country's top judge ordered that all those accused of graft in power generation projects be arrested and for the chairman of the anti-corruption National Accountability Bureau (NAB) to report to the court.

Coming as a populist cleric leads tens of thousands of protesters outside parliament to demand that the government resign, Tuesday's order sparked panic about an alleged judiciary-military plot to derail elections due by mid-May.

Interior Minister Rehman Malik threatened overnight to disperse the crowd unless leader Tahir-ul Qadri ends the demonstration, the largest political rally in the capital for years, but President Asif Ali Zardari later intervened to stop authorities from using force against protesters.

The rally has threatened to destabilise the nuclear-armed country as it inches towards what would be the first democratic transition of power between two civilian governments at the upcoming elections.

The economy is struggling, Taleban and other violence is at a high, the rupee is sinking, there is an energy crisis and fledgling peace gains with India appear in jeopardy following five deadly cross-border shootings in a week.

"The NAB chairman is going to appear before the Supreme Court tomorrow," NAB lawyer Aamir Abbas told AFP late on Wednesday.

Asked if any arrests were made so far, as ordered by the court, Abbas replied: "I am not aware about arrests." There was a heavy media presence outside the court on Thursday morning, with police stepping up security checks.

Commentators doubt that Prime Minister Raja Pervez Ashraf will be detained imminently given that the case has already been running for years.

Lawyers say that even if he is arrested for questioning over the allegations, which date back to his time as water and power minister, he can remain in office unless and until he is convicted.