Ukraine has banned Russian men between the ages of 16 and 60 years from entering the country.
Petro Tsygykal, head of the border service, disclosed this in a televised meeting on Friday.
“Today, the entry of foreigners is limited, primarily citizens of the Russian federation – non-admission of citizens of the Russian federation aged from 16 to 60, male,” Tsygykal said.
The move came amid fears of a Russian invasion after Russian forces seized three Ukrainian vessels and 24 sailors in the Black Sea on Sunday.
Ukraine said the incident was a flagrant violation of international law, while Russia says the vessels violated its territorial waters.
According to BBC News, an exception would be made for “humanitarian cases” such as those travelling to funerals.
The martial law has reportedly been imposed in 10 Ukrainian regions until December 26.
President Petro Poroshenko announced the restrictions after he met the country’s top security officials, including border guard chiefs, in Kiev.
Poroshenko said the ban was designed to prevent the formation of “private armies” in the country.
The president was said to be referring to Russian-backed separatists who formed units in April 2014 to fight Ukrainian government forces in eastern Ukraine.
Antonio Guterres, UN secretary-general, on Thursday said he hoped the international community could help calm tensions between Russia and Ukraine over the standoff.
Guterres urged Russia to respect “the territorial integrity of Ukraine avoid the worst”.
“I hope the situation can be contained without escalation and it is calling for international efforts for meaningful dialogue,” Guterres said.