General Ben Hodges, the commander of US ground forces in Europe, called on Russia Friday to expand media access to its upcoming military exercises, adding that Moscow's statements could not be trusted.
"If the Russian Federation is truly interested in stability and security, then be transparent, invite media to see everything that they do," Hodges told reporters in Lithuania.
Moscow has said 12,700 troops from Russia and Belarus will participate in the Zapad drills along the NATO's eastern flank from September 14 to 20.
However, western officials have said the preparations suggest it will be a much larger exercise, which would mean that Moscow should allow international observers to monitor the drills.
"The Russians have not given us a lot of reason to trust the numbers that they say," Hodges said, echoing remarks by NATO chief Jens Stoltenberg.
The exercises in western Russia and Belarus have caused unease in Poland and the Baltic states, though Moscow has insisted that they will be "purely defensive" in nature.
"I think this would all be solved and everybody would be relaxed if the Russian Federation would invite media to everything that they do the way that Lithuanian armed forces do, that German armed forces do, that American armed forces do," Hodges said.
Earlier this week the United States sent extra jet fighters and a company of US Army troops to beef up its presence in Lithuania during the drills.
NATO has also deployed about 1,000 soldiers in each of the Baltic states and Poland in response to growing concern over Russian intentions after Moscow's 2014 annexation of Crimea.
"I feel confident in the deterrence capability that's actually in this region. But we also have to always remain vigilant," Hodges said.
"Being alert is the responsibility for all of our security services. But I don't have a good record for predicting the future."