Russia has started military drills near its border with Ukraine.
Moscow said the exercises were in response to Ukraine’s escalating operations against pro-Russian separatists, as well as NATO exercises in eastern Europe.
Russian tanks were seen as close as eight kilometres from the border with Ukraine.
The Russian Defence Minister Serguei Shoigu said: “If this military machine is not stopped, it will lead to greater numbers of dead and wounded. Planned exercises by NATO forces in Poland and the Baltic countries do not foster normalisation of the situation surrounding Ukraine, either.”
Meanwhile NATO has begun beefing up its presence in central and eastern Europe.
The Polish defence minister said Warsaw and Washington will announce the deployment of more US ground troops in Poland next week.
On Wednesday, five NATO warships took part in a “battle stations” exercises on the waters of the Baltic Sea.
The deployment comes as NATO continues to search for ways to de-escalate the situation in Ukraine.