Two US warships are due to arrive in the Black Sea this week amid an escalation in fighting in eastern Ukraine where government forces have battled separatist troops in a conflict Kyiv says has killed 14,000 people, Reuters reported.
The deployment comes as the US and some western countries sound the alarm over what they claim is a big and unexplained build-up of Russian forces close to Ukraine's eastern border and in Crimea. Russia has said it moves its forces around as it sees fit, including for defensive purposes.
Russian Foreign Minister Sergei Lavrov, on a visit to Egypt, said Washington, not Moscow, had questions to answer about its activities in and around Ukraine.
"Questions are being asked about what Russia is doing on the border with Ukraine," said Lavrov. "The answer is very simple. We live there, it's our country. But what is the United States doing thousands of kilometers from its own territory with its warships and troops in Ukraine?"
Russian Deputy Foreign Minister Sergei Ryabkov was cited by Russian news agencies on Tuesday as warning US warships in the Black Sea to keep their distance, saying the risk of unspecified incidents was very high.
"There is absolutely nothing for American ships to be doing near our shores, this is purely a provocative action. Provocative in the direct sense of the word: they are testing our strength, playing on our nerves. They will not succeed," Ryabkov was cited as saying.
"We warn the United States that it will be better for them to stay far away from Crimea and our Black Sea coast. It will be for their own good."
Turkey said on Friday that Washington, which has provided arms to Ukraine, would send two warships to the Black Sea this week. The Pentagon declined to discuss Turkey's comments but said the military routinely sends ships to the region.
Russia's Black Sea Fleet is based in Crimea and it has powerful missile and radar facilities on the peninsula.