Ukraine’s border guard service says some 100 Russian male nationals were stopped from entering the country on December 1.
The news comes a day after President Petro Poroshenko announced that Russian male nationals between 16 and 60 years of age would be denied entry to Ukraine during a 30-day period of martial law that was approved by parliament earlier in the week.
The move comes amid escalating tensions between Kyiv and Moscow after Russian coast guard boats on November 25 opened fire and captured three Ukrainian naval vessels and their 24-member crew off Crimea, the Ukrainian Peninsula that Russia illegally annexed in 2014.
Ukrainian border guard spokesman Andriy Demchenko told Ukrainian TV on December 1 that the "vast majority" of those barred from entering Ukraine "couldn’t confirm the purpose of their trip to Ukraine."
He said that "some of them didn't have the necessary documents to enter Ukraine and others had exceeded the period of stay in our country."
In explaining the move a day earlier, Poroshenko said it was aimed at preventing undercover Russian military units from entering the country.
Russia said it had no plans to mirror the Ukrainian move. Foreign Ministry spokeswoman Maria Zakharova blamed the Ukrainian government on November 30 for implementing a policy that hurts ordinary people.
On November 29, Poroshenko said that Kyiv would impose "restrictions" on Russian citizens in Ukraine and the country's border guard said only Ukrainian nationals would be allowed to travel to Crimea in connection with the imposition of martial law for 30 days in parts of the country.
Ukrainian Foreign Ministry spokeswoman Kateryna Zelenko confirmed to RFE/RL by phone on November 30 that foreign journalists are among those excluded from entering Crimea from Ukraine but said her ministry was discussing whether to grant them an exception.
The official confirmation came hours after Anna-Lena Lauren, a Moscow-based foreign correspondent of the Swedish newspaper Dagens Nyheter, was barred by Ukrainian border guards from entering Crimea via what Ukraine deems the only legal route.
A Russian government-appointed ombudswoman in Crimea said on November 30 that the captured Ukrainian naval personnel had transferred to Moscow.
A Russian activist later that day said she had visited some of the Ukrainian sailors in a Moscow jail.
Russian TV station Dozhd on November 30 quoted Kogershyn Sagiyeva -- a member of the Moscow oversight council which is allowed to inspect prisons -- as saying that 21 seamen had been transferred to the Moscow Lefortovo jail while three others are in a hospital in another jail.
She said she met with some of the sailors and they appeared to be in good shape.
Russia says the Ukrainians had violated its border while Ukraine says its ships were acting in line with international maritime rules.
A Crimea court earlier this week ruled to keep the Ukrainian seamen behind bars for two months pending the outcome of the investigation.