The commission also announced the arrest on Friday of the former Nairobi County secretary, along with the former head of procurement.

Thirteen other people were also listed as suspects in the corruption case announced on Friday, and they were asked to present themselves at the nearest police station. These included members of the county’s tender evaluation committee, along with directors of several companies.

The governor is not the only nationally prominent politician recently arrested in the crackdown. In July, Finance Minister Henry Rotich was arrested on corruption charges related to a multimillion-dollar project to build two massive dams, becoming the first sitting cabinet member to be charged with financial misconduct in Kenya. Mr. Rotich has denied the charges.

But while Mr. Kenyatta has vowed to stamp out graft, critics have said that his administration isn’t serious about fighting corruption, calling it a mere public relations exercise. Efforts to tackle graft have also borne little results, according to the nongovernmental organization Transparency International.

Mr. Sonko, who was elected in 2017, is serving his first term as governor. He was a member of Parliament for the Madaraka constituency in Nairobi starting in 2010, and was elected as a senator of Nairobi County in 2013.

Nairobi, a city of about 3.5 million people, is both the capital of Kenya and the seat of Nairobi County. Besides being a financial hub for regional and global companies, it hosts dozens of embassies and consulates.

While Mr. Sonko has invited scrutiny for his showy lifestyle and colorful fashion, he has also drawn criticism for his management style. In November, lawmakers from Nairobi County said a “tragedy of untold proportions” was unfolding in the city, with poor public services and unpaid workers and suppliers. The leaders also criticized the governor for failing to appoint a new deputy after the previous one resigned in January 2018.