British Foreign Secretary Liz Truss warned Russia on Wednesday that it would be making a "grave mistake" if it attacked Ukraine and said London was working closely with its NATO allies to support Ukraine.
Ukrainian and U.S. officials have voiced concerns about a possible Russian attack on its neighbour, a suggestion the Kremlin has dismissed as false.
Earlier on Wednesday Russian fighter planes and ships practiced repelling air attacks on naval bases and responding with air strikes during military drills in the Black Sea, Interfax reported, as Ukraine also held combat exercises.
"We are very close allies of Ukraine and we are working with out partners in NATO but also directly with Ukraine to make sure they are fully supported," Truss told Reuters when asked about the possibility of an incursion.
"I think that would be a grave mistake from Russia."
(Reporting by Kylie MacLellan; editing by Guy Faulconbridge)
