There have been US flights near Kaliningrad recently.
There is a Russian territory on the Baltic sea.
An expert said that Russia renovated a nuclear weapons site in the middle of last year.
The US military appears to be stepping up aerial patrols of a Russian territory in Europe, potentially signalling concern that the Kremlin could use nuclear weapons in Ukraine.
On Wednesday, a Boeing RC-135 flew from a base in the United Kingdom to Kaliningrad, a Russian territory along the Baltic Sea that was annexed after World War II. There have been at least three such flights in the last week.
It is wedged between Poland andLithuania and provides the Kremlin with a forward operating base in NATO territory.
According to a nuclear arms expert at the Federation of American Scientists, Russia renovated a nuclear weapons storage facility in Kaliningrad, 50 kilometers from Poland. He wrote at the time that the facility could be used as a forward storage site that could be used in a crisis.
The Baltic Fleet in the Kaliningrad region conducted a "simulated missile strike exercise" using its Iskander operational and tactical missile complexes. Both nuclear and conventional missiles can be carried by Iskander missiles.
A request for comment from the US Air Force's European command was not responded to. According to a military fact sheet, the RC-135V/W provides "real time on-scene intelligence collection, analysis and dissemination capabilities" with its crew of as many as 30 people.
The flights around Kaliningrad are not groundbreaking or alarming, according to an expert on open-sourced intelligence gathering. He told Insider that there is an increased interest in Russian military movements by high-level decision makers in the US.
"This comes at a time when we are, as far as I can tell, at the closest point to nuclear war since 1983," he said.
According to five current and former US officials, Western intelligence agencies are stepping up efforts to detect any Russian military moves or communications that could signal the use of nuclear weapons in Ukraine.
Since ordering the invasion of Ukraine, the Russian leader has said that he could use nuclear weapons and warned that they are not bluffs.
"If the territorial integrity of our country is threatened, we will use all the means at our disposal to protect Russia and our people." Russian forces held a sham referendum in eastern Ukraine to justify annexing the territory and extend the definition of an attack on Russia to include land that has been conquered.
Robert Baer, a former CIA officer, told CNN that Putin was worried about the future of his regime and could be tempted to do the unthinkable.
The chances that he will use nuclear weapons are going up by the day.
Tell us about a news story. C Davis is the reporter for Insider.
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