The US, Britain, the EU, and Nato countries have expressed support for Ukraine
Two Ukrainian servicemen were killed by pro-Russian separatists in eastern Ukraine over the past 24 hours, Ukraine's military said on Tuesday, adding to already escalating tensions.
Kyiv says Russia has been building up its forces near Ukraine's eastern borders in recent weeks, and reports of separatist attacks on Ukrainian government forces have increased significantly.
Nato has said it is concerned about a Russian military build-up in the Donbas region, where Ukrainian troops have battled Russian-backed separatist forces in a conflict Kyiv estimates has killed 14,000 people since 2014.
Moscow and Kyiv have long accused each other of failing to implement a peace deal over the region.
The Kremlin said on Monday that Russian military movements near its shared border with Ukraine posed no threat to Ukraine or anyone else and that Moscow moved troops around its country as it saw fit.
The United States, Britain, the European Union, and Nato countries have expressed support for Ukraine.
The United States finds reports of Russian military movements on Ukraine's border "credible," has asked Moscow to explain the "provocations" and is ready to engage in the situation, the US State Department said on Monday.