British defense minister Gavin Williamson visited Ukraine on Friday where he told his Ukrainian counterpart that the Black Sea did not belong to Russia and that Britain had sent a Royal Navy ship there to show Kiev did not stand alone.

Williamson was speaking as tensions in the area remain high after Russia seized three Ukrainian naval vessels and their crews in the Black Sea last month, accusing them of illegally entering its territorial waters, a charge Ukraine denied.

Williamson on Friday met Stepan Poltorak, his Ukrainian counterpart, and visited the port of Odessa where a British Royal Navy ship, HMS Echo, docked earlier this week.

“The reason...that HMS Echo is here is that we firstly want to demonstrate the solidarity that we have with Ukraine and the fact that Ukraine doesn’t stand alone,” said Williamson.

“But also demonstrate our right to be able to come to ports such as Odessa, for freedom of navigation, for freedom for navies to be able to operate in the Black Sea. This isn’t Russia’s sea, this is an international sea.”

Relations between Moscow and Kiev have been locked in a downwards spiral since Russia annexed Crimea from Ukraine in 2014 and backed pro-Russian separatists in eastern Ukraine.