Russia and Ukraine on Wednesday held their first direct negotiations since March in a bid to break an impasse over grain exports that has seen food prices soar and millions face hunger.

The high-stakes meeting involving UN and Turkish officials in Istanbul broke up after slightly more than three hours without any immediate signs on a breakthrough.

The Turkish defense ministry issued a one-statement sentence saying the talks had "ended" and offering no hint as to whether progress had been achieved.

But the stakes could not be higher for tens of millions of people facing the threat of starvation in African and other poorest nations because of the battles engulfing one of the main grain producing regions of the world.

Ukrainian officials said at least five people died in Russian shelling on the region surrounding the Black Sea port city of Mykolaiv.

"You never get used to war. It's dreadful and scary," 60-year-old Lyubov Mozhayeva said in the partially destroyed frontline city of Bakhmut.

Ukraine is a vital exporter of wheat and grains such as barley and maize. It has also supplied nearly half of all the sunflower oil traded on global markets.

But shipments across the Black Sea have been blocked by Russian warships and mines Kyiv has laid to avert a feared amphibious assault.

Russian proposals

The Istanbul negotiations are being complicated by growing suspicions that Russia is trying to export grain it has stolen from Ukrainian farmers in regions under its control.

Russia authorities in Ukraine's southern region of Kherson on Wednesday countered with accusations that Kyiv's forces were deliberately burning crops and mining fields.

US space agency data released last week showed 22 percent of Ukraine's farmland falling under Russian control since the February 24 invasion.

The two sides entered the talks saying that a deal was close but some contentious issues remained.

Ukrainian Foreign Minister Dmytro Kuleba said Kyiv was "two steps from an agreement with Russia".

Russian defense ministry spokesman Igor Konashenkov said Moscow had "submitted a package of proposals for the speediest practical solution" of the crisis.

Russia said on Tuesday its requirements included the right to "search the ships to avoid the contraband of weapons" -- a demand rejected by Kyiv.

Grain corridors

NATO member Turkey has been using its good relations with both the Kremlin and Kyiv to try and broker an agreement on a safe way to deliver the grain.

Turkey says it has 20 merchant ships waiting in the region that could be quickly loaded and sent to world markets.

A plan by the UN proposes the ships follow safe "corridors" that run between the known location of mines.

Kyiv has also asked that its vessels be accompanied by warships from a friendly country such as Turkey.

Experts say de-mining the Black Sea is a complex operation that could take months -- too long to address the growing global food crisis.

Kuleba said he did not think Moscow actually wanted to reach an agreement because proceeds from grain sales would help support a Western-backed government in Kyiv that the Kremlin brands as "Nazis".

"They know that if we start to export, we will get proceeds from world markets, and this will make us stronger," Kuleba said.

'Operational pause'

The talks in Istanbul precede a meeting in Tehran next Tuesday between Turkish President Recep Tayyip Erdogan and his Russian counterpart Vladimir Putin.

Erdogan's ultimate goal is to bring Putin and Ukrainian President Volodymyr Zelensky down to Istanbul for talks aimed at pausing the fighting and launching formal peace talks.

But the Ukrainian army warned this week that Russia was preparing to stage its heaviest attack yet on the Donetsk region -- the larger of the two areas comprising the Donbas war zone.

The Russian army has not conducted any major ground offensives since taking the last points of Ukrainian resistance in the war zone's smaller Lugansk region at the start of the month.

Analysts believe the Russians are taking an "operational pause" during which they are rearming and regrouping forces before launching an assault on Sloviansk and Kramatorsk -- Ukraine's administrative centre for the east.

Ukraine is trying to counter the Russians by staging increasingly potent attacks with new US and European rocket systems targeting arms depots.

US officials believe the Russians are trying to recoup their losses by negotiating to acquire hundreds of combat drones from Iran.