Turkish and American justice officials met on Tuesday to discuss Turkey's demands for the extradition of a U.S.-based cleric accused of masterminding last month's failed coup attempt.

The meeting came ahead of a visit to Ankara Wednesday by U.S. Vice President Joe Biden, during which he will discuss the extradition request and other issues.

During the talks, Turkish Justice Ministry officials would share with the visiting U.S. Justice Department and State Department officials "evidence and testimonies obtained until now" concerning Muslim cleric Fethullah Gulen's involvement in the July 15 coup, the ministry said in a statement.

Gulen, who has lived in the U.S. state of Pennsylvania for the past 17 years in self-imposed exile, has denied any connection to the coup attempt that claimed at least 270 lives.

The U.S. government has asked for firm evidence before considering extradition.

In Washington, State Department spokesman Mark Toner said Turkey has formally requested Gulen's extradition. But Toner said the request doesn't relate to the recent coup attempt in Turkey. He declined to provide any further details.

"We are now considering the merits of the request," Toner told reporters.

The Turkish ministry said officials have sent four files — amounting to a total of 6,382 pages — containing evidence and extradition requests compiled by courts in Istanbul, Ankara and the northwestern city of Bursa.

The government has declared a state of emergency and launched a massive crackdown on Gulen's supporters in the aftermath of the coup, raising concerns among Turkey's allies and human rights groups. Some 35,000 people have been detained for questioning and more than 17,000 of them have been formally arrested to face trial, including soldiers, police, judges and journalists. Tens of thousands more people with suspected links to Gulen have been suspended or dismissed from their jobs in the judiciary, media, education, health care, military and local government.

On Tuesday, the military extended the terms of hundreds of apparently trusted colonels. A high military council meeting regrouping military leaders and government ministers extended by two additional years the service terms of 434 colonels, the Defense Ministry announced. It said 586 other colonels were retired from the Turkish Armed Forces.