Moscow, 5 June 2023 (dpa/MIA) - A major Ukrainian offensive in the south of the Donetsk region on Sunday was foiled by Moscow, the Russian Defence Ministry has claimed.

"The adversary's objective was to break through our defense on [what it believes to be] the most vulnerable front sector," said Defence Ministry spokesman Igor Konashenkov, according to Russian state news agency TASS. "The enemy failed to perform its tasks and had no success."

He said the presumed offensive began on Sunday morning at five frontline sections. The information could not be independently verified.

Initially, there was no comment from Kiev. Ukrainian President Volodymyr Zelensky has repeatedly stressed that his country is ready for the long-announced counter-offensive to liberate its territories from Russian occupation.

Elsewhere, fighting flared up again in the Russian border region of Belgorod between the army and volunteer units fighting alongside the Ukrainians on Sunday.

A total of 4,000 people from hard hit areas are said to have been brought to safety.

Meanwhile, Russia's Defence Ministry said it had succeeded in preventing a "sabotage and reconnaissance group of Ukrainian terrorists" from crossing a nearby river.

For some time now, there have been repeated fights and attacks in the Belgorod region, for which Moscow blames Kiev.

Groups called "Russian Volunteer Corps" and "Legion of Freedom of Russia" are fighting for Ukraine, but are made up of Russian nationalists.

Several members of the Russian Volunteer Corps published a video on Sunday in which they claimed to have captured several soldiers from the Russian army. This could not be independently identified.

The group said it wanted a meeting with Gladkov, who appeared open to the idea but the meeting did not take place.

The group then said they would hand over the prisoners to the Ukrainian side, which had no initial reaction to this.

Meanwhile Polish media reported that Poles are also fighting against Russia in the Belgorod region.

The online news portals Polsatnews.pl and Wprost.pl reported on Sunday that there were mercenaries fighting on the side of the Ukrainian army under the name of the Polish Volunteer Corps.

The reports referred to the group's own messages on Telegram and a video allegedly showing soldiers on their way towards Belgorod.

According to Polsat, the Polish Volunteer Corps was founded in February. Initially, it fought alongside the Ukrainian army as an independent unit consisting only of Poles. In the meantime, the troop is also acting together with the Russian Volunteer Corps.

The Russian position in Belgorod came under attack from the head of the private army Wagner, Yevgeny Prigozhin, who spoke of "chaos" in the Defence Ministry.

If the ministry in Belgorod does not put things in order "as soon as possible", he would send in his mercenaries there, he said. Prigozhin is considered a confidant of Russian President Vladimir Putin.

Prigozhin was critical of Russia's position following its announced capture of the war-torn city of Bakhmut.

On Sunday, Prigozhin conceded that the Ukrainian armed forces had moved into positions in the city again - a triumph for Kiev, a new disaster for Moscow, as observers commented on social networks.

Prigozhin also made accusations on Sunday against the regular Russian army.

Prigozhin said on Telegram that soldiers had mined a road in May that his fighters had used to drive out of Bakhmut.

He also published a document purporting to be an operation log from last month, which mentions exchanges of fire between Wagner mercenaries and soldiers.

The allegations could not be independently verified. The Ministry of Defence in Moscow did not comment.

Earlier in the day, two cruise missiles fired by Russian forces hit an airfield in central Ukraine, while four others were downed by Ukrainian air defences, air force spokesman Yury Ignat reported.

"Out of six cruise missiles, four were destroyed by the air defences, and two unfortunately struck an airfield near Kropyvnytskyi," he said, without providing details of any damage caused.

Russian forces also launched five drones, three of which had been intercepted, Ignat said.