Earlier this year, Russia completed a 19-kilometer (12-mile) bridge across the Kerch Strait, prompting complaints from Ukraine that it was being used to delay its ships, exert political pressure and hurt the country’s economy.

Grain ports around the Sea of Azov include the Russian ports of Rostov-on-Don and Azov, as well as Berdyansk and Mariupol in Ukraine.

A UN Security Council meeting has been called for 16.00 GMT on Monday, according to U.S. Ambassador Nikki Haley. NATO has urged “restraint and de-escalation,” adding it fully supports Ukraine’s sovereignty and called on Russia to ensure unhindered access to Ukrainian ports in the Azov Sea.

The incident underscores the transport risks in a region that’s becoming an ever more important supplier of grain to the global market, and exports of commodities such as corn and wheat could fall if the situation worsens, said Cherry Zhang, an analyst with Shanghai JC Intelligence Co.