Russia has fired missiles and drones at Ukrainian ports that ship grain worldwide, making much of the Black Sea unsafe for navigation.

The U.S. claims ships are vulnerable, and ship owners are willing to transport Ukrainian grain over the Black Sea if they can reduce the risk.

Russia dropped out of a wartime pact the U.N. and Turkey established last year to protect shipping businesses to avert a worldwide food catastrophe.

Ukraine, together with Russia, is a major provider of wheat, barley, and vegetable oil to poor nations.

After the grain deal collapsed, Ukraine wrote to the U.N. International Maritime Organization to construct its own temporary shipping route and provide guarantees of compensation for damage.

Ships in the Black Sea risk exploding mines, port collateral damage, or being targeted, which Stawpert called a huge escalation.

The International Union of maritime Insurance, which represents national and international maritime insurers, said Russia’s warnings make it doubtful underwriters will cover that risk.

The International Group of P&I Clubs, which covers liability for 90% of the world’s seaborne goods, said the only way to limit risk was through insurance from the 12 companies that make up the International Group of P&I Clubs.

The International Transport Workers’ Federation’s seafarers division director said the question should be whether it’s too unsafe to send sailors to Ukrainian ports.