Pakistan's highest court has disqualified Prime Minister Yousaf Raza Gilani from office, in a move likely to throw the country into a fresh round of political turmoil.

The Supreme Court announced its decision Tuesday based on its earlier ruling that Mr. Gilani was guilty of contempt for refusing to reopen a corruption investigation of President Asif Ali Zardari.

Chief Justice Iftikhar Muhammad Chaudhry ruled that Mr. Gilani ceased to be prime minister on the date of his conviction on April 26.

The court has instructed President Zardari to take steps for the election of a new prime minister.

Late Tuesday, Mr. Zardari's ruling party organized an urgent meeting to discuss its actions following the court ruling. The meeting was expected to last several hours.

Under the constitution, the president must summon a joint session of parliament that will elect a new prime minister.