The United States has carried out multiple surveillance flights this week around Kaliningrad, a Russian exclave located on the Baltic Sea coast. The American spy planes are likely assessing Moscow’s nuclear weapons activity as the two sides step up threats and warnings over the ongoing war in Ukraine. 

During the past week, at least three Boeing RC-135s have circled Kaliningrad – a small piece of land sandwiched between NATO members Lithuania and Poland – according to data collected by flight tracking site RadarBox. The territory has become a potential flashpoint in recent months, as members of the US-led military bloc have threatened to cut it off from mainland Russia, with which it shares no border. 

Earlier this year, NATO announced that it would welcome Finland and Sweden into the alliance. Moscow warned it could increase its military presence in the region as a response to any future strategic weapons deployments within the territory of new members. All but two of NATO’s 30 signatories have formally approved membership for Stockholm and Helsinki, with Turkey and Hungary now the only remaining hold-outs.

Additionally, Russia and Lithuania’s relationship degraded after Vilnius blocked Moscow from transporting goods from the homeland to its exclave. After receiving threats from the Kremlin and pressure from the European Union, however, Lithuania relaxed most of the restrictions. 

The increased surveillance flights come as Western leaders voice concerns that Russian President Vladimir Putin could order a nuclear strike on Ukraine or one of its neighbors. Politico recently reported that Western intelligence agencies “are stepping up efforts to detect any Russian military moves or communications that might signal that Putin has ordered the use of nuclear weapons.”