A Russian fighter jet flew close to a US Navy plane operating over the Black Sea, but the manoeuver was considered safe, a Navy spokeswoman said Friday.

The Russian SU-27 came within about 20 feet (six meters) of a US Navy P-8A Poseidon anti-submarine plane while the US aircraft was conducting routine operations in international airspace Tuesday, according to Captain Pamela Kunze.

"The interaction lasted 65 minutes and was considered safe and professional by the P-8A's mission commander," she said in a statement.

Distance is only one variable that is considered when defining "safe and professional," she added.

Mid-air interceptions are routine in international air space, and Russian jets frequently scramble to fly alongside US spy planes in and around the Baltic Sea and elsewhere near Russia.

"Most interactions are safe and professional," Kunze said.