US spy planes appear to be monitoring a Russian enclave in Europe, possibly looking for signs of nuclear weapons activity

• In recent weeks, flight-tracking sites have spotted US surveillance flights near Kaliningrad.
• Kaliningrad is a Russian territory on the Baltic sea, separated from mainland Russia by Lithuania.

The US military appears to be stepping up aerial surveillance of a Russian territory in Europe, potentially signalling concern that the Kremlin could decide to deploy or even use nuclear weapons in Ukraine as Russian leaders have warned.

On Wednesday, a US electronic surveillance plane, the Boeing RC-135, departed from a base in the United Kingdom and circled around Kaliningrad, a Russian territory along the Baltic Sea — sharing no land border with the mainland — that was annexed after World War II, according to a flight tracking website. It was at least the third such flight in the past week.

Home to nearly 500,000 people, it is sometimes referred to as Russia's "unsinkable aircraft carrier" because it is wedged between Poland and Lithuania, essentially providing the Kremlin a forward operating base within NATO territory.

In 2018, Russia carried out a "major renovation" of an active nuclear weapons storage facility in Kaliningrad some 50 kilometers from Poland, according to Hans Kristensen, a nuclear arms expert at the Federation of American Scientists. The facility, he wrote at the time, could function "as a forward storage site that would be supplied with warheads from central storage sites in a crisis."

In April, the Russian military announced that its Baltic Fleet in the Kaliningrad region conducted a "simulated missile strike exercise" using its "Iskander operational and tactical missile complexes." Iskander ballistic missiles can carry both conventional and nuclear warheads.

The US Air Force's European command did not immediately respond to a request for comment. According to a military fact sheet, the RC-135V/W provides "real time on-scene intelligence collection, analysis and dissemination capabilities," with its crew — as many as 30 people — able to "detect, identify and geolocate signals throughout the electromagnetic spectrum."

Aram Shabanian, an expert on open-source intelligence gathering at the New Lines Institute in Washington, DC, said the flights around Kaliningrad are somewhat unusual but not "groundbreaking or alarming in an of itself." What they suggest, he told Insider, is that there is "an increased interest in Russian military movements by high-level decision makers in the United States."

"This comes at a time when we are, as far as I can ascertain, at the closest point to nuclear war since 1983," he added, referencing an incident where a Soviet early-warning radar system falsely reported an incoming US nuclear attack.

Politico reported this week that the US and its allies are increasingly concerned, noting that Western intelligence agencies "are stepping up efforts to detect any Russian military moves or communications that might signal that Vladimir Putin has ordered the use of nuclear weapons in Ukraine," citing five current and former US officials.

Since ordering the invasion of Ukraine, the Russian leader has repeatedly hinted that he could use nuclear weapons, including in a September 21 speech announcing a military draft in which he warned that such threats are "not a bluff."

"[I]f the territorial integrity of our country is threatened, we will certainly use all the means at our disposal to protect Russia and our people," Putin said. Days later, Russian occupying forces held a sham referendum in eastern Ukraine to justify annexing the territory — and extending the definition of an attack on Russia to Ukrainian forces reclaiming land that has been conquered since the start of the war.

Speaking to CNN, former CIA officer Robert Baer warned that Putin, fearing for the future of his regime following major setbacks in Ukraine, could be tempted to do the previously unthinkable.

"The chances of his using nuclear weapons — at least tactical nuclear weapons — is going up by the day," Baer said.

Have a news tip? Email this reporter: cdavis@insider.com