CIA Director John Ratcliffe is in Moscow, Russia, for meetings, according to sources familiar with the trip.

His visit was revealed after a U.S. Air Force C-17 transport plane and a U.S. diplomatic motorcade were spotted at a Moscow airport.

Neither the U.S. nor Russian governments has publicly confirmed the purpose of the visit, and the CIA has not commented.

The trip comes as U.S. intelligence warns that Russian President Vladimir Putin may be increasingly willing to test NATO and the Trump administration through provocative actions, CBS News has reported.

Ratcliffe’s visit also comes as U.S.-mediated peace talks between Russia and Ukraine remain largely stalled, while the CIA continues to play a role in U.S.-Russia negotiations and detainee exchanges.