ALSO SEE: The Occupiers Are Advancing Near Izium, Rubizhne and Popasna,
and in the Kherson Region

A Ukrainian counter-offensive pushed Russian forces 25 miles east of Kharkiv, Ukraine's second largest city, US officials said on Monday night.

They also said Russian gains in Donbas had been "minimal at best" and "quite frankly anaemic", and Vladimir Putin's troops appeared to be displaying a risk aversion to casualties.

A senior US defence official said: "They were hoping to get Kharkiv and hold it."

The official added that in areas of Donbas they were "moving in and then declaring victory, and then withdrawing their troops only to let the Ukrainians take it back.

"There's a casualty aversion that we continue to see by the Russians now."

The official said Russian advances in the Donbas were "very cautious, very tepid".

He said about 70 of the 90 155mm howitzers promised to Ukraine had now been delivered, along with tens of thousands of rounds, and training for Ukrainian soldiers.

Amid reports that General Valery Gerasimov, the head of Russia's armed forces, has been killed in Ukraine, US officials said that while he did visit the Donbas last week, they could not confirm reports he was wounded.

A senior US defence official said: "We can confirm he was in the Donbas. It's certainly possible that his trip was of a manner of oversight in trying to gauge for himself what was going on.

"What he learned, what he transmitted to his commanders, if anything, we just don't know. For several days last week he was in the Donbas. We don't believe that he's still there."

It came as British intelligence officials said Russia has lost a quarter of its invading army in its botched occupation of Ukraine.

Some of Moscow's most elite units, including its Airborne Forces, have suffered the highest levels of attrition in the first 68 days of the conflict while one quarter of Russia's forces used in the invasion was now "combat ineffective".

The Kremlin has committed over 120 battalion tactical groups, each numbering between 600 to 1,000 soldiers, to Ukraine, which amounts to about 65 per cent of Russia's entire ground combat strength, according to the report.

The Ministry of Defence said it would "probably take years for Russia to reconstitute these forces".

On Sunday night, unconfirmed local reports from the southern port city of Odesa said that a 15-year-old boy was killed and a 17-year-old girl was injured in a Russian rocket attack.

The rocket, apparently aimed at a military facility, also damaged a nearby monastery.

Meanwhile, a Ukrainian drone destroyed two Russian patrol boats in the Black Sea off Snake Island, a rocky outcrop that became a symbol of Ukrainian resistance in the early days of the Russian invasion.

Footage released by the Ukrainian military shows the Turkish-made Bayraktar drone hitting the two Russian Raptor-class patrol vessels that can be used for landing troops.

The 40-acre island became famous when a tiny military unit posted on it refused to surrender to a Russian warship and famously told the vessel to “go f— yourself” on the first day of Moscow’s invasion, sparking a wave of Ukrainian patriotism.

Across the border in Belgorod, used as the Kremlin's staging post for its invasion, more explosions were reported on Monday after a series of unexplained attacks on infrastructure.

Meanwhile, Ukrainian authorities on Monday tried to evacuate a second group of civilians from Mariupol’s besieged Azovstal steel works after 100 people were able to leave the plant after taking shelter in its sprawling network of bunkers for several weeks.

Vadym Boichenko, the mayor of Mariupol, said on Ukrainian television that 100 people were able to leave the city’s basements on Monday and were awaiting an evacuation to a safe place.

“This is supposed to happen, and we’re waiting for the enemy troops to let it happen today.”

Authorities in the self-proclaimed separatist statelet of Donetsk said on Monday 214 people including 33 children left Mariupol that day for a separatist-controlled area.

Ukrainian officials did not confirm the reports.

The evacuation may have been complicated by reports of renewed shelling in the city.

Denys Shlega, a Ukrainian National Guard brigade commander in Mariupol, told Ukrainian TV that Russian forces on Sunday night started shelling the plant after a two-day break.

“There are still hundreds of civilians including about 20 children in Azovstal’s bunkers, according to our calculations,” he said.

Mr Putin, in response to numerous pleas to cease fire around the Azov Sea city that has been obliterated by weeks of Russian airstrikes, insisted in recent days that Russia was no longer shelling Mariupol.

Almost 24 hours after the first group of evacuees left Mariupol on Sunday, local officials in central Ukraine said that the people arrived safely.

“We have managed to evacuate over 100 women, children and elderly people,” the Ukrainian Armed Forces in Zaporizhzhia said on Monday.

“Everyone who has been evacuated will be offered a safe shelter in Zaporizhzhia. Finally people will be able to feel safe and have some rest.”

Mariupol authorities on Monday accused Russia of trying to cover up the traces of apparent war crimes in the city.

Petro Andryushchenko, an adviser to the mayor, claimed that Russian troops may have used lorries that brought in humanitarian aid to carry the bodies of killed civilians and take them out of town.

Bird-eye view drone footage shot by Russia-backed separatists showed white lorries parked at several bombed-out blocks of flats last week.

“We can say with certainty that the occupying forces are taking out thousands of dead bodies from Mariupol,” Mr Andryushchenko said.

“This is not an isolated case but a large-scale operation.”