BEIJING — Former rising Chinese political star Sun Zhengcai was expelled from the ruling Communist Party and dismissed from public office Friday amid a corruption investigation.

Sun, the former top official in the mega-city of Chongqing, is the highest-ranking serving official to be ensnared by President Xi Jinping’s sweeping anti-corruption campaign, now in its fifth year.

The official Xinhua News Agency said the party’s 25-member Politburo had approved the latest actions against Sun at a meeting after reviewing a report of the investigation. That comes just three weeks before a major party congress held once every five years at which Xi is expected to be given a second five-year term as party leader.

The moves clear the way for Sun to be prosecuted, with a guilty verdict all but certain. The party has said only that Sun is accused of “serious violations of discipline,” shorthand for corruption.

Sun, 53, sat on the Politburo and had been seen as a candidate for promotion to the body’s Standing Committee, the select group of leaders who constitute the apex of political power in China.

He was removed suddenly from his Chongqing post and replaced by protege Chen Min’er, who is tipped to be promoted to the Politburo, but not its Standing Committee.

Sun had been identified most closely with the China Youth League faction associated with Xi’s predecessor, Hu Jintao, which Xi has effectively sidelined in the succession process. His expulsion will help ensure that Xi’s supporters will hold strong majorities on both the Politburo and the smaller Standing Committee.