"We have deep concerns when there is an unsafe manoeuvre," Xinhua news agency quoted Pentagon as saying in a statement.
According to the statement, a Russian SU-27 Flanker first maintained a distance of 30 feet, then closed to within 10 feet of the US P-8A Poseidon electronic signals aircraft. The intercept occurred at 11.20 a.m. and lasted approximately 19 minutes.
"These actions have the potential to unnecessarily escalate tensions between countries, and could result in a miscalculation or accident which results in serious injury or death," said the Pentagon.
In response, Russian Defence Ministry said Russia had to scramble Crimea-based SU-27 fighter jets to intercept US spy planes making attempts to approach the Russian airspace over the Black Sea while flying with switched-off transponders, according to a Sputnik report.
"On Sep 7, 2016, US Navy P8 Poseidon reconnaissance aircraft made two attempts to approach the Russian airspace over the Black Sea while flying with switched off transponders," the report quoted Russian Defence Ministry's spokesman Maj. Gen. Igor Konashenkov as saying.
It was not the first time for such encounters between Russian and US warplanes or ships in 2016. In June, the two countries traded accusations over who was to blame for ships from each country getting dangerously close to each other in the Mediterranean Sea. In January, the Pentagon accused a Russian fighter jet flew within 15 feet of a US reconnaissance plane over the Black Sea.
