U.S. military officials have complained that a Russian fighter jet came dangerously close to a U.S. surveillance plane in the Mediterranean Sea, the second such encounter in four days in the region.
In its statement on Sunday, the U.S. Navy did not say where exactly the encounter occurred, only that it happened over international waters.
Several aircraft tracking sites said the incident occurred in the eastern Mediterranean, not far from the Syrian coast.
The Russian Su-35 fighter jet approached the P-8A plane twice on Sunday, and during the second time, it came within 8 meters of the U.S. plane, the Navy said.
"The second intercept was determined to be unsafe and unprofessional," it said.
A similar encounter occurred in same vicinity on April 15, the Navy said.
The Russian Defense Ministry issued a statement on Facebook on Monday, confirming the encounter and saying the Sukhoi jet was dispatched from the Hmeimim air based to meet the U.S. plane, but gave no further details.
The P-8A Poseidon is an anti-submarine, anti-surface-warfare plane.
Russia has a sizable naval contingent based at the Syrian port of Tartus, in support of Russian air and ground operations in Syria.
U.S., NATO, and Russian planes routinely engage in cat-and-mouse flying encounters around the world.
Russian long-range bombers regularly fly close to NATO member borders and U.S. surveillance planes frequently skirt Russian waters in the Baltic and Black seas, monitoring and probing Russian defenses.