A ship loaded with Ukrainian grain is on its way to Lebanon from a port on the Black Sea, following an internationally brokered deal to resume agricultural exports.

Agricultural products have been stuck at Ukrainian ports on the Black Sea due to a blockade by the Russian military. Turkey and the United Nations brokered a deal between Russia and Ukraine to resume the exports.

The first ship carrying Ukrainian grain since the Russian invasion left the port of Odesa on Monday.

Turkey's defense ministry says the ship loaded with corn will arrive in the waters off Istanbul on Tuesday night and will have cargo inspections on Wednesday.

Ukrainian President Volodymyr Zelenskyy said 16 more vessels are waiting to depart. He called for caution against "the illusion that Russia will simply refrain from trying to disrupt Ukrainian exports."

A US think tank, the Institute for the Study of War, said on Monday that Russian forces are transferring troops from the Donetsk region to support defensive positions in southern Ukraine.

The British defense ministry has pointed out that the Russian military is strengthening its forces in Ukraine's southeastern regions.

The Ukrainian military is stepping up its offensive with weapons including the High Mobility Artillery Rocket Systems, or HIMARS, provided by the United States with the aim to retake control of the southern regions.