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.

Neither Washington nor Moscow has publicly explained the aircraft's presence in Russia.

The Kremlin told Reuters it had no information about the flight, leaving uncertainty over who or what was aboard.

Aircraft flew from Latvia to Moscow

The aircraft's flight history showed that it arrived in Riga on August 23 after departing from Camp Springs, Maryland, where Andrews Air Force Base is located.

Andrews is a major US military installation and serves as a key hub for transporting senior American government officials.

It is also associated with Air Force One operations.

However, the aircraft's departure from the area does not establish that a senior US official was travelling aboard it.

C-17 aircraft are routinely used to transport personnel, vehicles, communications equipment and other logistical material.

They can also be deployed ahead of visits by senior officials to prepare transport and other infrastructure.

The unusual flight nevertheless drew considerable attention online because direct US military flights into Russia are rare amid the continuing conflict in Ukraine.

Speculation over possible US-Russia talks

The Moscow landing comes against the backdrop of renewed speculation about possible US diplomatic engagement with Russia over the Ukraine war.

There has been speculation in recent weeks that US Defence Secretary Pete Hegseth could travel to Moscow as Washington seeks to revive negotiations that have made little progress.

US President Donald Trump has also shifted his attention towards the Iran war, while discussions between Washington and Moscow over Ukraine have remained stalled.

Reports last week said US and European officials had been working on a new proposal for Moscow as efforts to advance negotiations continued.

Another theory circulating online linked the aircraft to a possible visit by US special envoys Jared Kushner and Steve Witkoff.

The War and Military News website suggested that the Globemaster's arrival could be connected with preparations for another round of talks in Moscow.

There was no official confirmation that either Kushner or Witkoff was aboard the aircraft.

Kushner and Witkoff previously travelled to Moscow

The last direct flight by a US aircraft to Russia reportedly took place in January, when Witkoff and Kushner travelled to Moscow for talks with Russian President Vladimir Putin.

The discussions focused on possible avenues towards ending the Ukraine conflict.

During those talks, Putin maintained his demand that Ukraine withdraw its forces from the eastern Donbas region as part of any settlement.

The latest aircraft movement has therefore attracted attention because of the previous use of US government-linked transport in connection with diplomatic missions to Moscow.

Kremlin says it has 'no information'

Kremlin spokesman Dmitry Peskov said on Tuesday that there were no plans for meetings with representatives of the US administration in Moscow during the week.

The Kremlin also told Reuters that it had no information about the US aircraft's arrival.

The absence of an official explanation has added to speculation surrounding the flight, although the presence of a C-17 alone does not establish that a diplomatic delegation or senior US official was aboard.

The aircraft is specifically designed for long-range transport of troops, vehicles, military equipment and other cargo, making it capable of supporting a wide range of missions.

Prisoner exchange theory emerges

Another possibility raised in reports was that the aircraft could be linked to a diplomatic arrangement or prisoner exchange.

The i Paper reported speculation about a potential exchange, following the release of former US Marine Robert Gilman earlier in August and other prisoner exchanges earlier this year.

There was no official confirmation connecting Tuesday's flight with any prisoner transfer.

Theories about a possible secret diplomatic channel have emerged as formal Russia-Ukraine peace negotiations remain deadlocked and Washington continues to explore ways to bring the conflict towards an end.

For now, the precise purpose of the US military aircraft's unusual journey from Riga to Moscow remains unclear.