Russia or its proxies are flying surveillance drones over routes that the United States and its allies use to ferry military supplies through eastern Germany, collecting intelligence that could be used to bolster the Kremlin’s sabotage campaign and assist its troops in Ukraine, according to U.S. and other Western officials.

U.S. and German officials have been discussing Russian sabotage efforts, including information that led to the arrest in May of three Ukrainian men accused in a Russia-linked plot, the officials said.

The Russian sabotage campaign has led to fires at warehouses in Britain, an attack against a dam in Norway, attempts to cut cables under the Baltic Sea and an array of operations intended to bring the war in Ukraine closer to the heart of Europe and to undermine support for Kyiv.

After hitting a high last year, Russian sabotage acts have fallen off significantly this year, experts and Western intelligence officials said. That is at least partly the result of heightened security in Europe, and efforts by U.S. and European intelligence services to prevent attacks.

The drop also likely reflects a swirl of diplomatic activity to negotiate an end to the fighting in Ukraine.

“The landscape is more difficult for Russians to operate,” said Seth Jones, who studies the issue for the Center for Strategic and International Studies. “But it’s not unreasonable to assume the Russians are a bit more cautious now while there are negotiations.”