Spying activity is often driving tensions between NATO and Russia. This is the case in the Baltic right now, where US and British surveillance planes are very visibly active around the Russian exclave of Kaliningrad.
The surveillance is being conducted by RC-135W, planes that conduct electronic surveillance, surveying the electromagnetic spectrum in the area to gather intelligence.
Kaliningrad was historically Ostpreußen, a part of Germany, and before that Prussia. The Soviet Union took the land in 1946 after WW2. The exclave loomed large around the start of WW2, as the lack of a land connection between Ostpreußen and the rest of Germany was the source of a lot of tension with Poland. Germans were expelled by the Soviets, and Soviet citizens were moved in in the late 1940s.
During the Cold War, Kaliningrad was physically connected to the rest of the Soviet Union through the Baltic States, but with them now independent and in NATO, the exclave is unconnected, and often a target of NATO exercises.
From a strategic perspective Kaliningrad is used to monitor NATO operations, and Russia often threatens to deploy arms, including nuclear weapons, in Kaliningrad to counter US deployments in central Europe.
Very active surveillance, like the kind the US and Britain are conducting, would be considered a provocation if Russia was doing it, and probably will be considered provocation by Russia since it’s being done to them.
NATO is almost always needling Russia in the region, building up ever-growing numbers of troops in the Baltic states and conducting growing military exercises, centered around engagements against Russia in general and Kaliningrad in particular.