U.S. Army Europe Commander Lieutenant General Ben Hodges said in an interview with Germany's Die Zeit, Censor.NET reports citing Radio Free Europe/Radio Liberty.
According to him, the Russian forces could capture Estonia, Latvia, and Lithuania "quicker than we could get there to defend them."
The article from the newspaper's June 22 edition also quotes Hodges as saying he agreed with an assessment by military analysts that says Russian forces could seize the capitals of the Baltic states within 36 to 60 hours.
NATO announced last week that it would deploy four battalions to Estonia, Latvia, Lithuania, and Poland to counter a more assertive Russia, ahead of a summit in Warsaw next month.
Russia says the presence of NATO troops close to its borders is a threat to its security.
Relations between NATO and Moscow have reached their lowest point since the Cold War over Russia's annexation of Ukraine's Crimean Peninsula in March 2014 and its support for separatists in the country's east.