Gabrovsky disappeared on March 9 and his body was found buried in the woods in Ukraine's central Cherkasy region close to the town of Zhashkov.
"Obviously it is concerning to us, these reports, but we need to learn more and know more before we are in a position to speak to it," Kirby stated. "We are just seeing them, and it’s just too soon for us to draw any kind of conclusion here or to make any statement. We need to learn more from the Ukrainian authorities about it."
In May 2015, Russian nationals Yevgeny Yerofeyev and Alexander Alexandrov were detained near a front-line town in the Luhansk region in eastern Ukraine. The Kiev authorities claimed the two detainees were active-duty Russian army servicemen.
The Russian Defense Ministry dismissed the claims, but acknowledged that Alexandrov and Yerofeyev had received military training in the Russian Armed Forces in the past, yet claimed they were not on active duty at the time of the arrest. Moscow has demanded that Kiev releases the two prisoners.