India, Aug. 25 -- A US military aircraft landed at Moscow's Vnukovo Airport on Tuesday, triggering speculation over the purpose of the unusual flight at a time of heightened tensions between Washington and Moscow over the Ukraine conflict.

Flight-tracking data and several reports indicated that the aircraft was likely a Boeing C-17 Globemaster III, a heavy-lift transport aircraft operated by the US Air Force to carry personnel, military equipment and other cargo over long distances.

The aircraft, operating under callsign RCH4555 and carrying registration 07-7181, departed Riga, Latvia, at around 8.50 am and landed in Moscow shortly after 10 am, according to flight-tracking data.

The reason for the flight was not immediately known.

The...