Turkish police on Wednesday arrested Istanbul Mayor Ekrem Imamoglu, a key political rival of President Recep Tayyip Erdogan, as part of an investigation into alleged corruption and links to terrorism.

Mr. Imamoglu was arrested in a highly coordinated operation in which Istanbul police closed roads in anticipation of protests following his detention, according to reports. Mr. Imamoglu is being held at police headquarters in Istanbul.

In a video posted to social media after his arrest, Mr. Imamoglu harshly criticized the Erdogan regime but called for optimism among his supporters. He added that the government was “usurping” the rights of the people.

“We are facing great tyranny, but I want you to know that I will not be discouraged,” he said in Wednesday’s video.

The arrest adds to an already turbulent week for Mr. Imamoglu, who has had his home searched and his university diploma revoked. Istanbul University nullified Mr. Imamoglu’s diploma on Monday, citing issues with the transfer of his records from a private university in northern Cyprus.

Without a valid university degree, Mr. Imamoglu cannot run in public elections under Turkish law. That is a problem for Mr. Imamoglu’s party, the Republican People’s Party, which was expected to nominate the mayor as its presidential candidate later this month.

“Currently, there is a power in place to prevent the nation from determining the next president,” said party Chairman Özgür Özel. “We are facing an attempted coup against our next president.”

• Vaughn Cockayne can be reached at vcockayne@washingtontimes.com.