The Russians are blocking 94 civilian vessels carrying food supplies in the Black Sea region and have already bombed three civilian vessels carrying goods from Black Sea ports around the world - in particular one chartered by an agricultural company
Source: Wendy Sherman, United States Deputy Secretary of State
Details: About 30% of the world's wheat is typically exported from the Black Sea region, as well as 20% of corn and 75% of sunflower oil.
It was specified that many shippers are wary of sending their ships to the Black Sea now, including to Russian ports.
According to Sherman: "The Russian Navy is blocking access to Ukraine’s ports, essentially cutting off exports of grain. They are reportedly preventing approximately 94 ships carrying food for the world market from reaching the Mediterranean."