Ukrainian sea drones attacked a Russian navy base near the Black Sea port of Novorossiysk, a major hub for Russian exports, early on Friday and were destroyed by Russian warships, Russia’s defence ministry said.

The attack prompted the Novorossiysk port to temporarily halt all ship movement, according to the Caspian Pipeline Consortium which operates an oil terminal there.

Russian social media users reported hearing explosions and gunfire near Novorossiysk on Friday morning. If confirmed it would be the first Ukrainian attack on one of Russia’s main commercial ports.

The Caspian Pipeline Consortium which loads oil onto tankers in Novorossiysk said the port has temporarily barred all ship movement. It said its facilities had not been damaged and oil loadings continued onto tankers which were already moored

Videos posted on a local online community and circulated by Russian online news outlet Astra showed the movement of ships just off the coast with the sound of gunfire coming from the direction of the sea.

The emergency services of Novorossiysk have confirmed reports of blasts and security services have been informed, Russia’s RIA news agency reported. The port is one of the biggest in the Black Sea.

The Caspian Pipeline Consortium is the main exporter of Kazakh crude.

Clashes in the Black Sea and adjacent ports have escalated since Russia refused last month to extend a deal allowing for the safe exports of grain from Ukrainian ports; Russian drones and missiles have struck several Ukrainian port facilities and grain silos on or near the Black Sea.

Russia has also reported an attack by Ukrainian sea drones on its warships which were escorting a civilian vessel.

Russian air defences downed 10 Ukrainian drones over Crimea on Friday morning and suppressed three more with electronic countermeasures, TASS cited the Russian defence ministry as saying.