Tensions are rising between Kyiv and Moscow over reports of Russian military manoeuvres on the border with Ukraine.
Unverified footage posted on social media appears to show Russian tanks being moved to areas that include annexed Crimea and territories controlled by Moscow-backed separatists.
It comes after the OSCE's Special Monitoring Mission to Ukraine reported hundreds of ceasefire violations in recent days - including 493 in the Donetsk region on March 26, mostly small-arms fire.
John Kirby, the Pentagon press secretary, said Russian operations led to the deaths of four Ukrainian soldiers in the eastern part of the country and the wounding of two others.
Ukraine's foreign minister Dmytro Kuleba urged Moscow to "cease the military escalation" and "immediately and unconditionally reaffirm its commitment to a ceasefire regime."
Russia however responded that it's free to deploy its armed forces on its own territory as it chooses - claiming that the manoeuvres aren't posing any threat to anyone.
On Thursday, foreign minister Sergey Lavrov said that "most military officials understand that any action aimed at unleashing a conflict would be detrimental", adding he was hoping Russia was "dealing with grown-up people, who realise the risks that are linked to further escalation of this confrontation."
How likely is a Russian offensive, and where would it be focused on?
Peter Dickinson, editor of UkraineAlert at the Atlantic Council think tank, told Euronews that a Russian invasion of Ukraine can't be completely excluded.
"In 2014 no one believed Ukraine could be invaded, or that east Ukraine could be invaded, and they were. You can't rule anything out."
"Russia and Ukraine can't find any sort of common ground at all", he continues, "the peace process has stalled to an almost complete deadlock".
"When Ukrainian president Volodymyr Zelenskyy was elected in 2019 there were hopes in Moscow, it seems, that there would be more flexibility on the Ukrainian side, but the country has remained quite tough in its position", he says.
Dickson believes that if an invasion was actually to happen, "the most logical threat would be probably to the south of Ukraine".
More precisely, in "the so-called land bridge between the area of occupied eastern Ukraine and Crimea itself, in an attempt perhaps to connect those two enclaves within Ukraine to create a more continuous mass of area controlled by Russia".