US called the encounter an unsafe and unprofessional naval maneuver by one of Russia's warships.

The United States said on Friday it would lodge a formal diplomatic "demarche" protest to Russia over what it called an unsafe and unprofessional naval maneuver by one of its warships in the East China Sea.

"We'll have military-to-military conversations with the Russians, and of course we'll demarche them, but to me safety at the end of the day is the most important (part)," acting U.S. Defense Secretary Patrick Shanahan told reporters outside the Pentagon.

"It will not deter us from conducting our operations."

Russia, in turn, has accused the U.S. warship of being at fault.