Ukraine's border service says that around 100 Russian citizens have been denied entry into the country since an entry ban for adult Russian males was announced.

Border guards' spokesman Andrei Demchenko has told Ukrainian television Saturday that "the vast majority of (them) 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."

President Petro Poroshenko announced Friday that all Russian males aged 16 to 60 would be banned from entering Ukraine during a 30-day period of martial law approved Monday.

Poroshenko said the move was intended to prevent undercover Russian military units from entering the country after Russia seized three Ukrainian naval vessels and their crews.