A second shipment of Ukrainian wheat reached Turkey via the Black Sea on Sunday, according to maritime traffic monitoring sites, despite Russian threats to attack boats heading to or from its neighbour and enemy.
The Palau-flagged bulk carrier Aroyat -- laden with 17,600 tonnes of wheat -- left the port city of Chornomorsk on Friday bound for Egypt.
Ukraine is testing a new sea route that avoids using international waters and follows those controlled by NATO members Bulgaria and Romania, following Russia's withdrawal from a UN-backed grain export deal.
According to the websites Marine Traffic and Vessel Finder, the Aroyat was at the southern exit of the Bosphorus Strait at 0300 GMT on Sunday.
It was to head towards the Dardanelles Strait to reach the Mediterranean.
A first ship loaded with 3,000 tonnes of wheat, and also flying the flag of Palau, left Chornomorsk without incident on Tuesday and arrived in Istanbul on Thursday.
Russia and Ukraine are two major agricultural powers whose supplies are crucial for global food security.
Moscow's invasion of its neighbour in February last year -- and subsequent international sanctions -- have destabilised global supplies and markets.
Ukrainian forces have been aiming to undermine Moscow's military control of the Black Sea, including with attacks on Russia-annexed Crimea.
Sevastopol, home to Russia's Black Sea fleet, has been targeted by increasingly frequent drone and missile attacks, with Kyiv claiming to have damaged several Russian warships.