A Russian warship caught the U.S. Navy guided-missile destroyer USS John S. McCain operating illegally in Russia's territorial waters in the Sea of Japan, but chased it off, Russia's defence ministry said on Tuesday.
Moscow said that the Admiral Vinogradov, a Russian destroyer, had verbally warned the U.S. ship and threatened to ram it in order to force it to leave the area.
The US ship had immediately returned to neutral waters after being warned off, the defence ministry said in a statement.
Such incidents are rare, but underscore poor diplomatic and military relations between Russia and the United States whose ties are languishing at a post-Cold war low.
The Russian ship, from the Pacific Fleet, had been tracking the American destroyer, which Moscow said had violated Russia's territorial waters at 0317 GMT by going two kilometres beyond the sea border.
The incident took place in the Peter the Great Gulf, it said.
The U.S. destroyer made no further attempts to enter Russian waters after leaving the area, said Moscow. But it said the Admiral Vinogradov was continuing to observe its movements and that another vessel, a corvette, had been dispatched to the area.
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