U.S. Army Europe commander Lieutenant General Ben Hodges said on Thursday, Censor.NET reports citing Reuters.
General Hodges told Reuters in an interview that allied officials would keep a close eye on military equipment brought in to Belarus for the Zapad 2017 exercise, and whether it was removed later.
"People are worried, this is a Trojan horse. They say, 'We're just doing an exercise,' and then all of a sudden they've moved all these people and capabilities somewhere," he said.
Hodges said he had no indications that Russia had any such plans, but said greater openness by Moscow about the extent of its war games would help reassure countries in eastern Europe.
NATO allies are nervous because previous large-scale Russian exercises employed special forces training, longer-range missiles and unmanned aerial vehicles.
Such tactics were later used in Russia's annexation of Crimea in 2014, its support for separatists in eastern Ukraine and in its intervention in Syria, NATO diplomats say.
Hodges said the United States and its allies had been very open about a number of military exercises taking place across eastern Europe this summer involving up to 40,000 troops, but it remained unclear if Moscow would adhere to a Cold War-era treaty known as the Vienna document, which requires observers for large-scale exercises involving more than 13,000 troops.