More than 50 ships are now waiting in the Bosphorus for permission to go to Ukrainian ports and load grain, Russia is trying to stifle the Ukrainian economy and slow down the flow of food, U.S. Ambassador to Ukraine Bridget Brink has said.

"Right now, more than 50 ships are waiting at the Bosphorus for approval to go to Ukrainian ports to load grain that will feed those who need it. Russia is trying to choke Ukraine's economy and slow the flow of food instead of abiding by the terms of its agreement," the ambassador said on Twitter.

She said that last month they managed to ship lifesaving wheat to Yemen, a shipment funded by USAID, Spain and France in support of the Grain from Ukraine initiative.

"This grain will feed 4 million people, showing how the Black Sea Grain Initiative enables Ukraine's farmers to feed the world," the U.S. ambassador said.