A Russian landing ship has been destroyed and two other vessels have been damaged in the occupied Ukrainian port city of Berdyansk, say, Ukrainian officials.
The Ukrainian military posted footage early on Thursday and said the Orsk had been hit by its forces.
Details of what caused the explosion and fire onboard the ship are unclear.
Berdyansk, which is west of the besieged port of Mariupol, was seized four days after Russia invaded Ukraine.
Russia says it has used the port as a base to ferry in equipment for its troops.
Russian army TV hailed the arrival of the Orsk in Berdyansk last week as an “epic event” as it was the first Russian warship to dock there.
Drone footage filmed by Russian state TV reporter Murad Gazdiev showed an armoured personnel carrier being offloaded from the Orsk in the port. The armoured vehicles were to be used to reinforce Russian troops, the TV report added.
Video posted by the navy and on social media showed explosions and a big ship on fire at the port at 07:00 (05:00GMT) on Thursday.
While the Orsk was said to have been destroyed, fire reportedly spread to other vessels as well as an ammunition depot and a fuel terminal in the port. Footage from the scene appeared to show two ships sailing at speed from the port.
Deputy Defence Minister Hanna Malyar told Ukrainian TV that the military had hit a “huge target”, capable of carrying 20 tanks, 45 armoured vehicles and 400 troops.
The BBC cannot independently verify the claim. Earlier this week Gazdiev, who works for Russia-backed media outlet RT, reported that Ukrainian missiles had repeatedly targeted Berdyansk port, and every missile had been intercepted by Russian anti-air defence.
Berdyansk is of major strategic value to the Russians, lying between Crimea and the besieged city of Mariupol, some 80km (50 miles) to the east, where an estimated 100,000 people remain stranded facing Russian bombardment.
Some of those who have managed to escape Mariupol have arrived in Berdyansk and Ukraine’s deputy prime minister has said they will be taken inland to the city of Zaporizhzhia.
Capturing the towns of Berdyansk and Melitopol are part of Russia’s bid to create a land bridge from Crimea to the Russian border, as well as establishing a route towards Zaporizhzhia.
Residents have staged protests against Russia’s occupation of Berdyansk, and video posted on social media this week showed the military beating people in an attempt to disperse the crowd.
Ukrainian officials said the attack on the Orsk had further symbolic value, suggesting that it may have taken part in Russia’s original capture of Crimea in 2014, pointing to medals apparently awarded to the ship’s commander and a crewman.