CIA director John Ratcliffe made a surprise visit to Moscow after US intelligence reportedly uncovered plans by Russia to test NATO’s resolve, amid growing fears that the Kremlin could be preparing for a fresh military mobilisation linked to the war in Ukraine.

Mr Ratcliffe made his first public trip to the Russian capital on Tuesday, according to The Wall Street Journal, as Washington assessed the risk of Moscow escalating its confrontation with the West.

The newspaper reported that US intelligence indicates Russia is planning to test NATO. Mr Ratcliffe is understood to have potentially met Vladimir Putin during the visit to warn the Russian president against such a move.

The CIA director also reportedly urged Ukraine to halt strikes inside Russia during his trip, according to reports.

His presence in Moscow emerged after a US Air Force Boeing C-17A Globemaster III transport aircraft and a diplomatic motorcade were spotted at an airport in the Russian capital.

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Flight-tracking data showed US Air Force flight RCH4555 entering Russia from Latvia. Flightradar24 subsequently reported that the “US Air Force C-17A Globemaster III flew from Riga to Moscow’s Vnukovo Airport”.

The extraordinary visit comes as concern mounts over increasingly frequent Russian military incursions into the airspace and waters of European countries, including NATO members.

Russian aerial drones recently penetrated Moldovan and Romanian airspace, while a naval drone was destroyed close to a natural gas platform off Romania on August 20.

The incidents have raised fears that Moscow is becoming increasingly willing to accept the risk of its war against Ukraine spilling directly into neighbouring countries.

The Institute for the Study of War said the pattern demonstrated that the Kremlin has “accepted the risk that its war against Ukraine will cause damage to other states, including NATO states”.

The ISW wrote: “Romanian authorities did not specify the origin of the naval drone, but Romanian Defense Minister Radu-Dinel Miruță stated that the naval drone was not Ukrainian.

“Such incidents are likely an intended consequence of Russian strike packages that now take Russian unmanned systems so close to the airspace or waters of NATO states and Moldova that the drones regularly cross these boundaries.”

Moldovan President Maia Sandu has also accused the Kremlin of deliberately sending some drones into Moldovan and NATO airspace, arguing that Russian intent can be assessed from the trajectory of the weapons.

The ISW cautioned that it could not establish whether every incursion was deliberate, but warned that the cumulative effect was significant.

“ISW is unable to confirm the intent of Russian drone incursions into the airspace of other states, but the net effect of these incidents normalizes the incursion of Russian weapons into and damage within Moldovan and NATO territory,” the institute said.

It added that Russia could prevent such violations by redesigning its strike packages and moving the trajectories of its strike vehicles away from NATO and Moldovan territory.

“Russian forces could prevent such violations of other states’ sovereign airspace and waters by redesigning their strike packages and moving strike vehicle trajectories away from NATO and Moldovan territory.”

The ISW said the failure to make such adjustments, combined with the increasing frequency of the incidents, pointed to a deliberate attempt by Moscow to make incursions against Western territory appear routine.

“That Russian forces have not adjusted their strike campaigns, along with the increasing frequency of these incidents, indicates that the Kremlin intends to normalize these violations against NATO.”