Russia on Friday dismissed as inflammatory a media report suggesting Moscow might be weighing an attack on Ukraine and accused the United States of making a series of aggressive moves in the Black Sea.

Washington has raised concerns about a potential Russian attack on Ukraine with its European Union allies, the Bloomberg news agency reported a day earlier.

The report cited potentially suspicious troop movements inside Russia as being one of the reasons for U.S. concern.

The Kremlin said it was up to Moscow alone where it deployed its forces within its borders.

"Such headlines do nothing more than pointlessly and groundlessly fuel tensions. Russia does not pose a threat to anyone," Kremlin spokesman Dmitry Peskov told reporters on a conference call.

Washington has publicly said it is concerned by "unusual Russian military activity" near Russia's border with Ukraine. Peskov said such concerns were wide of the mark.

"We have repeatedly said that the movement of our armed forces on our territory should not be a cause for concern," Peskov said.

Regional tensions have mounted this week as the European Union accused close Russian ally Belarus of encouraging thousands fleeing war-torn parts of the world to try to cross its borders. Brussels has threatened to impose sanctions.

Russian and Belarusian paratroopers held joint drills on Friday in western Belarus near its border with Poland, the countries' defense ministries said.

Russia's Ministry of Defence said it had detected six flights by NATO spy planes in the airspace over the Black Sea, part of what it described as intensifying air reconnaissance by Western military aircraft.

The Russian military also said it was tracking U.S. naval ships in the Black Sea and accused Washington of studying the region as a potential theater of war.

"We regard the aggressive U.S. military activity in the Black Sea region as a threat to regional security and strategic stability," the military said in a statement.

Russia annexed Crimea from Ukraine in 2014 and says the waters around it belong to Moscow now despite most countries continuing to recognize the peninsula as Ukrainian.

Russian-backed separatists took control of Ukraine's eastern Donbass region that same year and soldiers on both sides continue to be regularly killed in the conflict there.