MEXICO CITY  Mexico’s former senior antidrug official has been arrested and accused of accepting bribes from a drug cartel, the authorities said Friday.

Noé Ramírez Mandujano, who as the chief of Mexico’s organized crime unit was the closest equivalent to the government’s drug czar, was arrested late Thursday after questioning, said Attorney General Eduardo Medina-Mora.

Mr. Ramírez is the highest-ranking official to come under suspicion in a purge of the police and prosecutors for possible ties to drug traffickers. While he led the unit, known by its Spanish initials as the Siedo, Mr. Ramírez met twice with a member of a loose federation known as the Pacific Cartel and took a payoff of $450,000, Mr. Medina-Mora said.

In return, Mr. Ramírez passed along information about investigations and actions against the cartel, Mr. Medina-Mora said. The witness who accused Mr. Ramírez of taking the bribe told investigators that more money had also been promised to him.