Russia late Sunday admitted that it seized three Ukrainian vessels off Crimea after they ignored the "demands to stop", according to the country's federal service. 

“Berdyansk”, “Nikopol” and “Yany Kapu” vessels didn’t respond to the Russian border service's demands to stop, and therefore, Russian military "had to use the weapons to stop them", FSB said in a statement. 

FSB said Russia has launched a criminal investigation into the "violation of the Russian state border.”

Three Ukrainian sailors suffered non-life threatening injuries during the incident, and they received medical treatment, it said. 

The Ukrainian Navy earlier accused Russia of opening fire on its warships off Crimea, asserting that crew members were wounded and its vessels were seized by Russia.