It came as Kerry was on his way to Kiev to meet with the new Ukrainian leadership that deposed a pro-Russian president, and has accused Moscow of a military invasion in Crimea.
The Kremlin, which does not recognize the new Ukrainian leadership, insists it made the move in order to protect Russian installations and its citizens living there.
On Tuesday, Russian troops who had taken control of the Belbek air base in the Crimea region fired warning shots into the air as around 300 Ukrainian soldiers, who previously manned the airfield, demanded their jobs back.
About a dozen Russian soldiers at the base warned the Ukrainians, who were marching unarmed, not to approach.
They fired several warning shots into the air and said they would shoot the Ukrainians if they continued to march toward them.
The shots reflected tensions running high in the Black Sea peninsula since Russian troops—estimated by Ukrainian authorities to be 16,000 strong—tightened their grip over the weekend on the Crimean peninsula, where Moscow's Black Sea Fleet is based.
