"The last Urals cargo from Ust-Luga was loaded on Apr. 24. The next one was expected to start loading on the same date, but the buyer refused loading," a trader on the Urals market told Reuters.

"Today the next cargo should have started loading, but it hasn't yet," the trader added.

The last cargo that was loaded from Ust-Luga port was of Surgutneftegaz crude for loading on Apr. 23-24, which was purchased by Total, traders said.

A cargo from Kazakh producers scheduled for loading on Apr. 24-25 was not shipped, nor the next, from Rosneft, scheduled for loading on Apr. 25-26, traders said.