Pakistan's Supreme Court has ordered the arrest of Prime Minister Raja Pervez Ashraf and 15 others over corruption allegations.
Mr Ashraf denies accepting bribes when approving power generation projects as minister for water and power in 2010.
Analysts say the timing of the court order is suspicious, but the move is unlikely to lead to the prime minister's immediate removal.
Earlier on Tuesday, a populist preacher who is believed to be backed by the military, led thousands of protesters in Islamabad, demanding that the government resign. They are camped near parliament.
Muhammad Tahirul Qadri recently returned from Canada to lead a call for reforms.
Mr Ashraf's predecessor, Yousuf Raza Gilani, was forced out as prime minister last June after the Supreme Court convicted him of contempt for failing to pursue a corruption case against the president. Mr Ashraf was appointed in his place.
The Supreme Court order said the prime minister and the others should be arrested and produced before court within 24 hours. But correspondents say the prime minister's lawyers may find ways of delaying any appearance.
There was no immediate statement from the government. President Asif Zardari was holding a meeting of leading figures in the Pakistan People's Party in Karachi, according to state broadcaster PTV.
General elections are due in May, but no date has been announced.
Qadri has said he wants the military and judiciary to be install a caretaker government to oversee the elections.