President Barack Obama and Turkish President Tayyip Erdogan have discussed the status of US-based cleric Fethullah Gulen, blamed by Turkish authorities for masterminding a recent failed coup, during a call, the White House says.
The Turkish Government has filed material in electronic form about Mr Gulen with the US government, which has been waiting for a formal extradition request, White House spokesman Josh Earnest said on Tuesday.
US officials have said Turkey must provide proof that Mr Gulen was involved in the coup attempt.
Any extradition request from Turkey, once submitted, would be evaluated under the terms of a treaty between the two countries, Mr Earnest said.
Mr Obama offered US assistance for Ankara's investigation into the attempted coup and pressed Mr Erdogan to proceed according to the democratic principles outlined in Turkey's constitution, Mr Earnest said.
"The principles of democracy should be adhered to even as a thorough investigation is conducted," he said.
The US State Department said it was still in the process of analysing the documents submitted by Turkey and could not characterise them as an extradition request for Mr Gulen.
Mr Gulen, a 75-year-old former ally of Mr Erdogan, has lived in self-imposed exile in Pennsylvania since the late 1990s. He has denied any involvement in the abortive coup.
Earlier, Turkey's Justice Ministry it had sent a dossier to the United States on Mr Gulen, but did not make clear whether that amounted to an official extradition request.