Ukraine has accused Russia of ramming one of its boats off the coast of Crimea, amid rising naval tensions.
A Ukrainian navy statement says the “openly aggressive actions” occurred as three of its vessels sailed to Mariupol in the Sea of Azov.
Its tug, named Yana Kapu, allegedly suffered damage to its engine, guard rail and outer shell.
But Russia said the ships were in its waters, and accused the Ukrainians of “provocative actions”.
The Sea of Azov lies east of the Crimean peninsula, which was annexed by Russia in 2014, and south of regions held by pro-Russian separatists.
Russia said the Ukrainian ships – two warships named as the Berdyansk and the Nikopol, and the tug – were trying “to create a conflict situation in this region”.
The ships “illegally entered a temporarily closed area of Russian territorial waters”, Russia’s state security service the FSB reportedly said in a statement.
But Ukraine said it had informed the Russians of its plan to move its ships through the sea to Mariupol.
The navy statement said the Russian actions marked a breach of the UN Convention on the Law of the Sea .
Tensions have risen in the seas off Crimea in recent months.
While both countries promised free access to the Sea of Azov, Russia has increased its military presence and inspections, with some calling its actions an “economic blockade” of Ukraine’s Azov ports in the east of the country.
More than 10,000 people have died in the eastern Donetsk and Luhansk region since separatists moved against the Ukrainian state in April 2014.
Russia annexed the Crimean peninsula the month beforehand.
Ukraine and the West accuse Russia of sending its troops to the region and arming the separatists.
Moscow denies this, but admits that Russian “volunteers” are helping the rebels.