Hulking ships carrying Ukrainian wheat and other grains are backed up along the Bosporus in Istanbul as they await inspections before moving on to ports around the world.

The number of ships sailing through this narrow strait, which connects Black Sea ports to wider waters, plummeted when Russia invaded Ukraine 10 months ago and imposed a naval blockade. Under diplomatic pressure, Moscow has begun allowing some vessels to pass, but it continues to restrict most shipments from Ukraine, which together with Russia once exported a quarter of the world’s wheat.

And at the few Ukrainian ports that are operational, Russia’s missile and drone attacks on Ukraine’s energy grid periodically cripple the grain terminals where wheat and corn are loaded onto ships.