By Pavel Polityuk and Aleksandar Vasovic
KIEV/MARIUPOL Ukraine (Reuters) - Ukraine said one of its naval vessels came under artillery attack from the shore on Sunday, in what pro-Russian rebels claimed as the first sea victory of their separatist war.
"A Ukrainian border patrol cutter in the Azov Sea was attacked from the shore today. Artillery was used. A rescue operation is under way," Ukrainian military spokesman Andriy Lysenko told Reuters.
A Ukrainian military officer who asked not to be named said: "It appears that a ship has been damaged, I do not know who exactly fired on it and with what."
No further details were available on the vessel and the number of crew on board.
"The militia have dealt the enemy their first naval defeat," Igor Strelkov, a separatist military commander who stepped down in mid-August, said on the social media network VKontakte.
Photographs and videos posted on Strelkov's page showed footage shot from the shore looking out to sea, where thick black smoke was visible on the horizon. It was not possible to confirm their authenticity.
The separatists, who want to break away from Ukraine and join Russia, have been fighting Ukrainian government forces since April in a conflict that has killed some 2,600 people.
Sunday's attack came days after the rebels opened a new front, breaking through to the shore of the Azov Sea in Ukraine's southeast corner. Ukraine and its Western allies attributed the sudden rebel advance to help from Russian tanks and troops, something Moscow continues to deny.
(Reporting by Pavel Polityuk and Aleksandar Vasovic; Writing by Mark Trevelyan, editing by Rosalind Russell)