Here's a report from RFE/RL's Ukrainian Service on the Sea of Azov incident:
Ukraine: Russian Ship Rams Navy Tugboat In Sea Of Azov
Ukraine says a Russian coast guard vessel has rammed one of its navy tugboats off the Moscow-annexed Crimean Peninsula in "openly aggressive actions," resulting in damage to the ship.
The Ukrainian Navy said the incident took place on November 25 as three of its ships including two small warships were transiting from the Black Sea port of Odessa to Mariupol in the Sea of Azov, via the Kerch Strait between Crimea and Russia.
Russia's Federal Security Service (FSB), which oversees the country's border guard service, accused Kyiv of illegally entering its waters and deliberately provoking a conflict.
The Sea of Azov has been an area of heightened tensions between Moscow and Kyiv since Russia seized Ukraine's Crimea region in March 2014 and shortly thereafter began supporting separatists in the eastern Ukrainian regions of Donetsk and Luhansk in a conflict that has killed more than 10,300 people.
A 2003 treaty between Russia and Ukraine designates the Kerch Strait and Sea of Azov as shared territorial waters.
However, Moscow has been asserting greater control over the passage in the past several years, particularly since it opened a 19-kilometer-long bridge linking Crimea with Russian territories across the Kerch Strait in May.
Both sides have recently increased their military presence in the Azov region, with Kyiv accusing Moscow of harassing ships heading for Ukrainian ports such as Mariupol.
A Russian border guard ship, the Don, "rammed into our tugboat," Ukraine’s navy said in a statement, adding that this caused damage to its engine, outer shell, and guardrail.
Russia's ships "carried out openly aggressive actions against Ukrainian naval ships," it also said, adding that its ships were continuing on their way "despite Russia's counteraction."
Meanwhile, the FSB said in a statement that the Ukrainian ships "illegally entered a temporarily closed area of Russian territorial waters.
It said that Ukraine’s ships were carrying out "provocative actions" and that their aim was to “create a conflict situation in this region."
It did not mention ramming the Ukrainian tugboat.
Ukraine said it gave Russian authorities advance warning of its ships' route.