Turkish authorities have prepared an official request for the temporary arrest of United States-based Islamic cleric Fethullah Gulen over his alleged involvement in the coup attempt on July 15, Turkey’s state-run Anadolu news agency said Saturday.

The request by the Istanbul Chief Public Prosecutor’s office claims it has determined the coup was staged upon orders by Gulen and requests that he be arrested prior to the submission of a formal extradition request.

The request has been submitted to Turkey’s Justice Ministry for it to be relayed to U.S. authorities, Anadolu said.

Ankara claims Gulen movement is responsible for the failed putsch which has left more than 270 people dead and has branded it a terrorist organization. It has demanded that its leader, who runs a network of worldwide charities and schools from self-imposed exile in Pennsylvania, be returned to Turkey to face trial.

Washington has said it would need evidence of the cleric’s involvement, and says the regular extradition process must be allowed to take its course. Gulen has denied involvement in the violent coup attempt.

On Friday, Turkey’s foreign and justice ministers announced that a four-person delegation from the U.S. Justice Department will be arriving on Aug. 22 and meet with their Turkish counterparts on the following two days to discuss the extradition request. Prime Minister Binali Yildirim announced on Saturday that U.S. Vice President Joe Biden would be visiting Turkey during that time, Anadolu said.

In Washington, The White House confirmed that Biden will travel to Turkey on Aug. 24. Biden typically meets with the premier of a foreign country when he visits. He has been one of the Obama administration’s key interlocutors with Turkey’s government, speaking frequently with President Recep Tayyip Erdogan.

Turkey has launched a massive crackdown on alleged supporters of the Gulen movement, raising concerns among European governments and human rights groups. More than 35,000 people have been detained for questioning while tens of thousands of others have been dismissed from government jobs, including in the judiciary, media, education, healthcare, military and local government.