Russian and Ukrainian officials were to hold talks in Istanbul on Wednesday over stalled grain deliveries that have pushed global food prices skywards, while Kyiv said it had destroyed a Russian arms depot as the war rages on.

Ukraine is one of the world's biggest exporters of wheat and other grain, but shipments have been blocked by both Russian warships and mines that Kyiv has laid across the Black Sea.

Turkey, which has spearheaded efforts to resume the essential grain trade, will host the talks, which will also be attended by a UN delegation.

AFP / Simon MALFATTO

On the ground, Kyiv said it had launched artillery that wrecked a Russian arms depot and also carried out a "special operation" to free military captives in the Moscow-controlled Kherson region.

Ukrainian military officials said the strikes on Tuesday had destroyed artillery, armoured vehicles "and a warehouse with ammunition" in the Russian-occupied town of Nova Kakhovka.

"The occupiers have already felt very well what modern artillery is and they will not have a safe rear anywhere on our land," President Volodymyr Zelensky said in his evening address.

Western officials and military analysts have warned the Ukraine conflict is morphing into a gruelling battle of attrition
Western officials and military analysts have warned the Ukraine conflict is morphing into a gruelling battle of attrition AFP / Anatolii Stepanov

Russian-backed authorities accused Ukraine of damaging civilian infrastructure and killing at least seven people.

"Warehouses were hit, as were shops, a pharmacy, petrol stations and even a church," the head of the city's Moscow-backed administration, Vladimir Leontiev, said on social media.

Ukrainian military intelligence also said its forces had freed five captives in the "special operation" in Kherson, including a military serviceman and former police officer, without specifying when.

A Russian strike on Donetsk over the weekend left dozens dead in one of the single-worst attacks recently in the war
A Russian strike on Donetsk over the weekend left dozens dead in one of the single-worst attacks recently in the war AFP / Anatolii Stepanov

The Ukrainian army has for several weeks been waging a counter-offensive to recapture Kherson, which was taken by Russian troops early in the invasion of Ukraine, which began in February.

The deputy head of the pro-Russian authorities in Kherson, Ekaterina Gubareva, said Ukraine had used long-range, precision artillery systems supplied by the United States in the strikes in Nova Kakhovka.

Western officials and military analysts have warned the Ukraine conflict is morphing into a gruelling battle of attrition
Western officials and military analysts have warned the Ukraine conflict is morphing into a gruelling battle of attrition AFP / Anatolii Stepanov

Military analysts are crediting newly arrived systems from the West -- including HIMARS from the United States -- with attacks deeper into Russian-controlled territory.

EU member states, which have been supplying Ukraine with military support, on Tuesday approved one billion euros ($1 billion) in financial help for Kyiv, billing it as the first instalment of a promised nine-billion-euro rescue package agreed in May.

The United States separately announced $1.7 billion for Ukraine to help fund recovery.

Map showing the situation in Ukraine, as of July 5 at 0700 GMT
Map showing the situation in Ukraine, as of July 5 at 0700 GMT AFP / Simon MALFATTO

"This aid will help Ukraine's democratic government provide essential services for the people of Ukraine," Treasury Secretary Janet Yellen said of the funds that are part of a $7.5 billion aid package signed by President Joe Biden in May.

Moscow advanced its offensive across Ukraine, with officials in the southern city of Mykolaiv saying Russian forces had bombed two medical facilities and homes, injuring 12 people.

Five people were injured in Russian shelling on Ukraine's second city Kharkiv, said regional governor Oleg Synegubov, after strikes the previous day left seven dead across that region.

But the heaviest fighting in recent weeks has centred on the Donbas where Moscow's forces have slowly made progress against fierce resistance since failing to capture Kyiv in nearly five months of fighting.

In Bakhmut -- one of the few remaining cities under Ukrainian control in Donbas -- AFP journalists heard nearby artillery fire.

"The front is getting closer," said municipal official, Dmytro Podkuyidko, estimating that more than one-third of the town's population of 73,000 have fled.

"If it gets worse, I'll end up leaving too," Podkuyidko said.

Turkey meanwhile announced the Wednesday talks between Moscow and Kyiv to try to break the impasse on allowing Ukrainian grain to leave its southern ports.

"Unblocking Ukrainian ports is one of the key components of global food security," Ukrainian presidential aide Andryi Yermak said on Telegram.

Turkish officials say they have 20 merchant ships waiting in the Black Sea that could be loaded quickly with Ukrainian grain.

A Russian foreign ministry spokesman stressed that Moscow was entering the meeting with a list of firm demands, including searching ships.

UN Secretary-General Antonio Guterres played down expectations heading into the talks, saying "we are working hard indeed, but there is still a way to go."

Top Russian officials did not attend the ceremony, which took place under a heavy police presence.