ANKARA, Turkey—Police launched a major corruption investigation in the Turkish cities of Istanbul and Ankara on Tuesday and detained at least 22 people, including prominent civil servants and the sons of two Cabinet ministers.

The simultaneous police raids appeared to target key allies of Prime Minister Recep Tayyip Erdogan.

The detained included the son of Economy Minister Zafer Caglayan, the son of Interior Minister Muammer Guler, the mayor of the Istanbul district of Fatih—a stronghold of Erdogan's party—and the CEO of state-owned Halk Bank, the state-run Anadolu Agency reported. The police also questioned prominent Istanbul developer Ali Agaoglu.

The agency said the investigation was focused on the alleged rigging of state bids and bribery, and it appeared to be aimed at the construction sector, which has been a major focus of the government and a key to Turkey's economic growth.

The governor of Istanbul confirmed that police had conducted an operation but declined to provide details. Police and prosecutors did not issue statements on the probe. Police did not return telephone calls requesting comment, and Interior Ministry officials said they had no immediate statement to make.

Erdogan said he would not comment on the raids "until the judicial process is complete." However, earlier Tuesday he made an impassioned speech at a ceremony in the central city of Konya that alluded to politically motivated "traps" aimed at bringing his government down.

"We won't bow to any threats," he said. "They may revert to dirty ways and set as many dirty traps as they like. Turkey is not a country that can be operated on. If they have any accounts to settle, if they have the confidence, there are elections on March 30. They should settle accounts there."

Those municipal elections are expected to be a vote of confidence in Erdogan's Islamic-based government, now into its 11th year in power.

Tuesday's investigation also came as Erdogan's Islamic-rooted governing Justice and Development Party is locked in an apparent power struggle with a moderate Islamic movement that is led by an U.S.-based cleric Fethullah Gulen. The movement is believed to have millions of followers in Turkey who have helped the governing party win three consecutive general elections since 2002.

The movement's followers are largely believed to have strong footholds in Turkey's police and judiciary, and analysts suggested that Tuesday's police raids are the Gulen movement's way of hitting back at the government after it threatened to close the movement's cram schools, which are a major source of its income.

The police probe "shows how serious the power struggle between the movement and the government has become," said Ali Tekin, a professor of political science at Yasar University in Izmir. "They are engaged in a struggle to determine the country's direction. It is a struggle about who will lead the country."

The company owned by Agaoglu, the Istanbul developer, said in a statement that the businessman had been questioned and company offices searched. Agaoglu has been behind some of the largest public works projects in Istanbul.


Desmond Butler in Istanbul contributed.