Western officials on Friday tried to coax Russia into allowing Ukraine to ship its grain out to the world as the four-month-old war threatened to bring hunger to countries far away from the battlefields.

Moscow, however, accused the West of waging economic warfare on Russia by attempting to isolate it with sanctions imposed over the Feb 24 invasion.

President Vladimir Putin warned that Russia's military operations in Ukraine had barely got started and the prospects for negotiation would grow dimmer the longer the conflict dragged on.

"We have heard many times that the West wants to fight us to the last Ukrainian. This is a tragedy for the Ukrainian people, but it seems that everything is heading towards this," Putin said in a speech to parliament on Thursday.

On the frontlines in Ukraine's eastern Donbas region, officials reported continued Russian shelling of towns and villages ahead of an anticipated new push to grasp more territory.

'Not your country'

At a meeting of G20 foreign ministers in Bali, Indonesia, some of the staunchest critics of the Russian invasion confronted the Kremlin's top diplomat Sergei Lavrov.

High on their concerns was getting grain shipments from Ukraine out of blockaded Black Sea ports. Ukraine is a top exporter and aid agencies have warned that countries in Africa, the Middle East and elsewhere face devastating food shortages if supplies do not reach them.

At a plenary session, US Secretary of State Antony Blinken urged Moscow to let Ukrainian grain out to the world, a Western official said.

"He addressed Russia directly, saying: 'To our Russian colleagues: Ukraine is not your country. Its grain is not your grain. Why are you blocking the ports? You should let the grain out,'" the official said.

Earlier, Lavrov had berated the West, saying that instead of focusing on how to tackle global economic problems at the meeting, ministers had embarked on "frenzied criticism" of Russia over the Ukraine conflict.

Indonesian Foreign Minister Retno Marsudi called on the G20 to "find a way forward" to address global challenges and said the repercussions of the war, including rising energy and food prices, would hit poor countries the hardest.

"It is our responsibility to end the war sooner than later and settle our differences at the negotiating table, not at the battlefield," Retno said at the opening of talks.

However, Putin's comments in Moscow indicated that the prospects of that happening were dim right now.

No sorrow

The biggest conflict in Europe since World War Two has killed thousands, displaced millions and flattened Ukrainian cities.

Russia says its "special military operation" is intended to degrade Ukraine's military and root out people it calls dangerous nationalists. Ukraine and its Western backers say Russia is engaged in an unjustified land grab.

After failing to quickly take the capital Kyiv, Russia is now waging a war of attrition in Ukraine's industrial heartland of the Donbas, made up of the regions of Luhansk and Donetsk.

On Sunday, Moscow declared it had "liberated" Luhansk and now plans to capture parts of neighbouring Donetsk it does not control.

Luhansk governor Serhiy Gaidai said on Friday Russian forces were indiscriminately shelling villages, towns and cities.

"They hit houses, every building that seems to them a possible fortification. To move forward, do not count personal losses and do not feel sorry for the inhabitants of the area," he said.

The situation was similar in settlements in Donetsk.

Vadym Lyakh, the mayor of Sloviansk in Donetsk, said a woman was killed overnight when Russian shelling hit a residential building.

Reuters could not independently verify the battlefield accounts.

Britain's defence ministry said Russian forces were likely to be pausing to replenish before undertaking new offensive operations in Donetsk. The ministry said Russia's immediate tactical objective might be Siversk, a small industrial city in the north of Donetsk.

Ukrainian President Volodymyr Zelensky, in his nightly video message, said the raising of the Ukrainian flag on Snake Island in the Black Sea on Thursday was a sign his country would not be broken.

Russia abandoned Snake Island, about 140km south of the port of Odesa, at the end of June – a victory for Ukraine that Kyiv hoped could loosen Moscow's blockade of Ukrainian ports.

"Let every Russian captain, aboard a ship or a plane, see the Ukrainian flag on Snake Island and let him know that our country will not be broken," Zelensky said.