Ukrainian forces hung on to positions in the ruined eastern city of Bakhmut while Moscow said its security forces were battling Ukrainian saboteurs who had taken hostages in a cross-border raid.
Moscow said a group of armed Ukrainians had crossed into Russia's Bryansk province, fired on a car killing one person and wounding a child, and were holding hostages in a shop near the border.
"We are talking about a terrorist attack. Measures are now being taken to destroy these terrorists," Kremlin spokesman Dmitry Peskov told reporters.
An aide to Ukrainian President Volodymyr Zelenskiy called the reports a false provocation by Russia, but also appeared to imply some form of attack had been carried out by partisans.
Near the front lines west of Bakhmut, in the Ukrainian-held town of Chasiv Yar, Reuters outgoing artillery fire was heard.
In nearby towns and villages, fresh trenches had been dug on the roadside 20-40 metres apart, an apparent sign that Ukrainian forces were strengthening defensive positions west of the city.
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The boss of Russia's Wagner private army, Yevgeny Prigozhin, released video of his men lifting a Wagner banner atop a semi-ruined multi-storey building, which he said had been filmed near the centre of Bakhmut. The Reuters news agency was not immediately able to verify the location of the footage.
Bakhmut has been reduced to a blasted wasteland, with a few thousand of its 70,000 pre-war civilian population still living inside as armies are involved in street-by-street battle.
Russian troops, bolstered by hundreds of thousands of reservists called up last year and tens of thousands of convicts recruited by Wagner from prison, have been advancing north and south of the city, to cut off the remaining routes in.
Moscow, which lost captured territory throughout the second half of 2022, says taking Bakhmut would be a step towards seizing the rest of the surrounding Donbas region, a major aim.
Kyiv says the city has limited strategic value, but it is holding on to exhaust Russia's invasion force in what has become the bloodiest battle of the war.
"Sooner or later, we will probably have to leave Bakhmut. There is no sense in holding it at any cost," Ukrainian member of parliament Serhiy Rakhmanin said, adding the aim was to "inflict as many Russian losses as possible".
debris by a road in the village of Sosnove, Donetsk region
The reported cross-border raid into Russia's Bryansk province comes days after Moscow said Kyiv had attacked targets deep inside its territory with drones.
"Today, a Ukrainian sabotage and reconnaissance group penetrated the Klimovsky district in the village of Lubechanye," Bryansk governor Alexander Bogomaz said on his Telegram channel.
"Saboteurs fired on a moving car. As a result of the attack, one resident was killed and a 10-year-old child was wounded."
Russia's RIA state news agency said several people had been taken hostage in a store in Lubechanye, less than 1km from Russia's border with northeastern Ukraine.
Zelenskiy aide Mykhailo Podolyak called the Russian reports "a classic deliberate provocation".
Moscow "wants to scare its people to justify the attack on another country & the growing poverty after the year of war," he tweeted.
But he also implied an attack was indeed under way, carried out by Russian partisans: "Fear your partisans," he wrote.
massive outages because it had refused to capitulate to Moscow's war demands
Russian missiles crashed into a five-story apartment block in the southern city of Zaporizhzhia overnight, collapsing upper floors in the centre of the building.
As dawn broke, rescue workers were seen carry the body of a man out of the wreckage. Police said at least four people had been killed. Residents, in shock, were being kept warm aboard a bus while crews tried to clear the debris.
"The people were screaming from under the rubble," Yuliia Kharytenko, 36, said. "We ran out in whatever we were wearing. Our cat is left there, scared. We don't know if it is alive".
damaged or removed in the year since Russia invaded
An international team of war crimes investigators said today that the Russian state had funded and operated a network of at least 20 torture chambers during its eight-month occupation of Kherson, recaptured last year by Ukrainian forces.
Russia's aim was to "subjugate, re-educate or kill Ukrainian civic leaders and ordinary dissenters", the team said.
Moscow has denied abusing civilians in occupied areas and intentionally targeting them in attacks. The Kremlin did not immediately respond to a request for comment.
Russian forces are under pressure to secure advances now, before warmer weather brings the region's season of sucking black mud - "bezdorizhzhia" in Ukrainian, "raputitsa" in Russian - legendary in military history for destroying armies attempting to attack across Ukraine and western Russia.
Kyiv, for its part, is focusing on defence for now, planning a counteroffensive later this year with new weapons supplied by the West.
Western allies discussing 'security guarantees' with Kyiv
The war dominated a foreign ministers' meeting in New Delhi of the G20 group of big economies, one of the last international forums involving top western officials where Russia is still invited. US and European delegates are pushing for a statement that will contain condemnation of the war.
A senior US State Department official said Secretary of State Antony Blinken spoke for less than ten minutes to Russian Foreign Minister Sergei Lavrov on the meeting's sidelines, telling him Washington would back Ukraine as long as necessary.
"Unfortunately, this meeting has again been marred by Russia's unprovoked and unjustified war against Ukraine, deliberate campaign of destruction against civilian targets, and its attack on the core principles of the UN Charter," Mr Blinken told the meeting.
Chancellor Olaf Scholz said that Germany and its allies were in talks with Kyiv over future security guarantees in preparation of a sustainable peace for Ukraine.
"We are speaking with Kyiv and other partners over future security guarantees for Ukraine," Mr Scholz said in a speech to the German parliament.
"Such security guarantees, however, come with the presumption that Ukraine successfully defends itself in this war," he said, adding that Germany would continue to support Kyiv with weapons supplies.
Mr Scholz renewed calls for Russia to withdraw its troops from Ukraine and said President Vladimir Putin was not ready for talks over a "just peace" and an end to the war.
"Nothing suggests" Mr Putin would come to the negotiating table at the moment, Mr Scholz said.
He also used the speech to warn China against arming Russia in its war against Ukraine, following US claims that Beijing was considering such a move.
"My message to Beijing is clear: use your influence in Moscow to push for the withdrawal of Russian troops," Mr Scholz said.
