Russian Federal Security Service (FSB) says three Ukrainian navy vessels, which crossed the marine border on Sunday morning, are heading for Kerch strait that separates Crimea from mainland Russia.

“This morning at around 7 a.m. Moscow time, three vessels belonging to Ukrainian armed forces violated the United Nations Convention on the Law of the Sea… to enter Russian territorial waters,” read a statement from Russia’s federal security agency FSB, which is responsible for maintaining the country’s borders.

https://www.rt.com/news/444815-crimea-ukrainian-navy-territorial-waters/