Russia has deployed a reconnaissance ship to the eastern Mediterranean in a bid to "to gather current information in the area of the escalating conflict", a military source told Interfax news agency.
The ship is understood to have left the naval base in the Ukrainian Black Sea port of Sevastopol late on Sunday.
The Defence Ministry declined to comment on the reports.
More top news
Boris Johnson and David Davis quit Theresa May’s Cabinet over the Brexit plans, but a series of lesser-known names have also departed.
Thousands of people are expected to welcome the national football side home after their triumph in Russia.
Olivia Colman has taken on the role of the Queen for series three of Netflix's The Crown and the resemblance is striking.