A Russian warship Vasily Bykov fired warning shots and boarded a Palau-flagged cargo ship Sukru Okan in the Black Sea, Russia's Defense Ministry said..

The ministry said its warship fired the warning shots when the dry cargo ship failed to respond to a request to stop for an inspection on Sunday.

"To forcibly stop the vessel, warning fire was opened from automatic weapons," it said.

Russian soldiers boarded the vessel with the help of a Ka-29 helicopter.

"After the inspection group completed its work on board, the Sukru Okan continued on its way to the port of Izmail."

The ministry said cargo ship was heading towards the Ukrainian port of Izmail but Refinitiv shipping data showed shows the cargo vessel’s destination as the Romanian port of Sulina which is close to Izmail.

Tensions in Black Sea

It is the first time Russia has fired on a merchant ship outside Ukraine since Moscow pulled out of a UN-brokered grain deal last month.

After that, Russia said that it deemed all ships heading to Ukrainian waters to be potentially carrying weapons. Russia also struck Ukrainian grain facilities on the Danube.

Ukraine responded with a similar threat to ships approaching Russian or Russian-held Ukrainian ports. Ukraine also attacked a Russian oil tanker and a warship at its Novorossiysk naval base, next door to a major grain and oil port.

Mykhailo Podolyak, a senior adviser to Ukrainian President Volodymyr Zelenskyy said the incident was a "clear violation of international law of the sea, an act of piracy and a crime against civilian vessels of a third country in the waters of other states."

Ukrainian military doubts Russian report

Meanwhile, Natalia Humeniuk, spokesperson for the Ukraine's southern military command, stressed that other official sources had not confirmed the Russian statement.

"I believe that attention should be drawn to this and the peculiarities of hybrid warfare should be kept in mind," she said in televised remarks.

"This statement could be a signal to all civilian vessels in the Black Sea," she said, and called for all transportation and navigation there to be conducted under international guarantees.

Russia, she added, was trying to assert its right to stop a ship or deploy aircraft in the Black Sea and "face no consequences."