Turkey's foreign minister said Thursday he was "optimistic" a deal could be reached soon that addressed Russian concerns and allowed Ukrainian grain to flow across the Black Sea.

Mevlut Cavusoglu's comments came less than a day after Russian President Vladimir Putin set an unexpected new condition for resuming the blocked deliveries.

Up to 25 million tonnes of wheat and other grain have been blocked in Ukrainian ports by Russian warships and landmines Kyiv has laid to avert a feared amphibious assault.

The crisis has sent global food prices soaring and pushed millions of people in the world's poorest countries to the edge of starvation.

The first direct talks between the warring sides' military delegations since March -- attended in Istanbul last week by Turkish and UN officials -- came up with an initial draft for resolving the impasse.

The sides were meant to have met again this week for the possible signature of a formal agreement.

But no talks had been confirmed by Thursday and new demands from Moscow put the prospects of an imminent deal in doubt.

"We have hope for grain," Cavusoglu said in a televised interview. "We hope to give good news in the coming days."

Russian President Vladimir Putin said Tuesday that he expected any agreement to also address his own country's blocked grain exports.

The five-month war is being fought across one of Europe's most fertile regions by two of the world's biggest producers of grain.

Almost all of the grain is usually shipped out of the region across the Black Sea.

Cavusoglu acknowledged Putin's concerns.

"When we resolve this issue, not only will the export path for grain and sunflower oil from Ukraine be opened, but also for products from Russia," he said.

"Even if these Russian products are not affected by sanctions, there are blockages concerning maritime transport, insurance and the banking system," he said.

"The United States and the EU have given promises to lift these," he said. "I am optimistic."

NATO member Turkey has enjoyed good working relations with both Moscow and Kyiv throughout the conflict.