The Ukrainian border guards service said on Saturday Russia had closed off the northwestern part of the Black Sea to navigation.
"The presence of ships and ships in this zone will be regarded as a terrorist threat," it said in a statement.
On Friday, Ukraine said Russia had hit two commercial ships near the southern Ukrainian port of Odessa, one day after Russia began a full-scale invasion of Ukraine.
(Reporting by Pavel Polityuk; writing by Matthias Williams; Editing by Catherine Evans)
