A Russian warship on Sunday fired warning shots at a cargo ship in the southwestern Black Sea as it made its way northwards, the first time Russia has fired on merchant shipping beyond Ukraine since exiting a landmark United Nations-brokered grain deal last month.

Russia in July halted participation in the Black Sea grain deal that allowed Ukraine to export agricultural produce via the Black Sea and Moscow cautioned that it deemed all ships heading to Ukrainian waters to be potentially carrying weapons.

Russia said in a statement that its Vasily Bykov patrol ship had fired automatic weapons on the Palau-flagged Sukru Okan vessel after the ship’s captain failed to respond to a request to halt for an inspection.

Russia said the vessel was making its way towards the Ukrainian port of Izmail. Refinitiv shipping data showed the ship was currently near the coast of Bulgaria and heading towards the Romanian port of Sulina.

“To forcibly stop the vessel, warning fire was opened from automatic weapons,” the Russian defence ministry said.

The Russian military boarded the vessel with the help of a Ka-29 helicopter, the ministry said.

“After the inspection group completed its work on board, the Sukru Okan continued on its way to the port of Izmail,” the defence ministry said.

A Turkish defence ministry official said he had heard an incident had taken place involving a ship heading for Romania, and that Ankara was looking into it.

Reuters could not immediately reach the vessel or its owners for comment.

Ukraine did not immediately comment on the incident.

Black sea at war?

Firing on a merchant vessel will ratchet up already acute concerns among shipowners, insurers and commodity traders about the potential dangers of getting ensnared in the Black Sea — the main route that both Ukraine and Russia use to get their agricultural produce to market.

Russia and Ukraine are two of the world’s top agricultural producers, and major players in the wheat, barley, maize, rapeseed, rapeseed oil, sunflower seed and sunflower oil markets. Russia is also dominant in the fertiliser market.

Since Russia left the Black Sea grain deal, both Moscow and Kyiv have issued warnings and carried out attacks that have sent jitters through global commodity, oil and shipping markets.

Russia has said it will treat any ships approaching Ukrainian ports as potential military vessels, and their flag countries as combatants on the Ukrainian side.

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.

Ukraine and the West say Russia’s steps amount to a de-facto blockade of Ukrainian ports that threatens to cut off the flow of wheat and sunflower seeds from Ukraine to world markets.

Russia dismisses that interpretation and says the West failed to implement a parallel agreement easing rules for its own food and fertiliser exports.