Pakistan’s Supreme Court has issued an arrest warrant for the country’s prime minister Raja Pervez Ashraf for corruption.
The surprise move came as thousands marched in the capital Islamabad calling for reforms to clean up government.
Authorities have 24 hours to detain the prime minister and 16 others.
Big crowds showed their dissatisfaction with the current administration as they massed around the parliament complex.
The anti-corruption protests had been convened by a populist cleric, Tahirul Qadri, who wants the judiciary to ban corrupt politicians from standing in upcoming elections.
A spokesman said they would not leave until the current regime, which is backed by the United States, stands down.
At one point security forces fired into the air and used tear gas to try to control the crowd.
But though Qadri can mobilise large gatherings, he is not universally popular. Some see him as too close to the army, which has a history of military coups and interference in elections.