BEIJING — Sending tremors across China’s political landscape, President Xi Jinping and other party leaders have authorized a corruption inquiry against the powerful former head of the domestic security apparatus, Zhou Yongkang, according to sources with elite political ties.

It is the first time since the founding of the People’s Republic of China that an official who has held such high office has been the focus of a formal corruption investigation, and in pressing his antigraft crusade to new levels, Mr. Xi has broken a longstanding taboo. Mr. Zhou was once a member of the Communist Party’s top rung of power, the Politburo Standing Committee, and even retired members of that body have always been spared such scrutiny.

The principal allegations against Mr. Zhou emerged from investigations over the past year into accusations of abuse of power and corruption by officials and oil company executives associated with him. Those inquiries have already encircled his son, Zhou Bin, and other family members, the sources said.

Mr. Xi and other leaders agreed by early December to put the elder Mr. Zhou directly under formal investigation by the party’s commission for rooting out corruption and abuses of power, the sources said. They said a senior official went to Mr. Zhou’s home in central Beijing to inform him about the inquiry, and Mr. Zhou and his wife, Jia Xiaoye, have since been held under constant guard.