Ukraine's Russian-backed breakaway eastern territories have ordered military mobilisations amid a deadly escalation in fighting.
Men of fighting age in the self-declared people's republics of Donetsk and Luhansk are being put on stand-by.
Monitors report a "dramatic increase" in attacks along the line dividing rebel and government forces.
A Ukrainian soldier was killed by shelling on Saturday morning, the first such death reported in weeks.
In the German city of Munich, Ukrainian President Volodymyr Zelensky is due to meet Western leaders including US Vice-President Kamala Harris at a security conference.
US President Joe Biden says he is convinced Russia will invade Ukraine, an allegation Moscow denies.
Western nations have accused Russia of trying to stage a crisis in the breakaway regions to give it a reason to launch an offensive.
The US estimates there are 169,000-190,000 Russian personnel massed along Ukraine's borders, a figure that includes separatist fighters in Donetsk and Luhansk.