Belarus has started exporting diesel produced at its refineries to Russia's port of St. Petersburg for the first time, as it seeks new buyers after its usual exports to Ukraine were halted by the conflict there, according to traders and Refinitiv data.

Ukraine, which typically consumes more than 7 million tonnes of diesel a year, used to rely on Russia's ally Belarus for more than 40% of its diesel needs.

Belarus was left with excess supply when sales to Ukraine halted, traders said.

Belarus shipped 18,656 tonnes of diesel to St. Petersburg in April and plans to ship a further 125,000 tonnes in May, rail data on Refinitiv Eikon showed, under a transit deal with Russia.

It was not immediately clear who was supplying the fuel or who was the buyer.

But traders said shipping the fuel via Russia did not fully resolve the issue of extra supply because European Union sanctions imposed on the Belarus energy industry last year made it more difficult to secure a sale.

Russia and Belarus signed a transit agreement in March 2021 to ship up to 9.8 million tonnes of Belarusian oil products via the Russia's Baltic ports.

Belarus had been mostly shipping gasoline, fuel oil and vacuum gasoil, but until April it had not shipped diesel.

(Reporting by Reuters; Editing by Edmund Blair)