President Recep Tayyip Erdoğan and his Russian counterpart Vladimir Putin will discuss stalled exports of Ukrainian grain at their meeting in the Iranian capital on Tuesday, a Kremlin aid told reporters.

The talks come as officials from Russia, Ukraine, Turkey and the United Nations will most likely meet this week to discuss resuming Ukraine’s Black Sea grain exports, Ankara said on Monday, while a Turkish official said lingering "small problems" should be overcome.

Erdoğan is set to meet Putin, their first face-to-face talks since Russia launched its military campaign in February, when the two leaders are hosted by Iranian President Ebrahim Raisi in Tehran on Tuesday.

The talks are officially intended to focus on the situation in war-ravaged Syria.

But the Kremlin said Putin and Erdoğan will also hold a separate meeting that will focus heavily on Ukraine.

"The issue of Ukrainian grain shipment will be discussed with Erdoğan... We are ready to continue work on this track," Yuriy Ushakov, foreign policy adviser to Putin, said on Monday.

Russia’s invasion of Ukraine – two major global wheat suppliers – has sent prices for grains and other food products soaring. It has stalled Kyiv’s exports, leaving dozens of ships stranded and some 22 million tons of grain stuck in silos at Ukrainian ports.

Turkish Defense Minister Hulusi Akar last week said Russia, Ukraine, Turkey and the U.N. would sign a deal this week on the grain exports corridor after talks in Istanbul.

United Nations chief Antonio Guterres called last week’s summit a "critical step forward" but said there was still "a long way to go" before there would be peace talks to end the war.

"An agreement was reached on a plan, general principles for shipping grain and food products... A meeting on this within the week is probable," Akar said on Monday.

He said technical matters like forming a monitoring center in Istanbul, identifying safe routes and checkpoints at port exits and entries were on the agenda.

Separately, a senior Turkish official said there was a high probability the quartet would sign a deal this week.

"However there are a couple of small problems. Negotiations continue to overcome these," the official said, adding that any positive steps could be affected by an attack or other major developments occurring in the war.

"But there is a general expectation that it will be signed this week. I am quite optimistic. It won’t take long before a final agreement is reached," the person added.

At the weekend, Russia vowed to step up military operations in Ukraine as its rockets and missiles pounded cities.