Russian forces pounded frontline cities in eastern Ukraine with air strikes and artillery attacks, while US officials stepped up efforts to locate the source of a leak of classified US documents, including those on Ukrainian counter-offensive plans.

The Russians pressed on with their offensive in the eastern Donetsk region where several cities and towns came under heavy bombardment, Ukraine’s general staff said on Tuesday.

Ukrainian forces repelled several attacks, it said, as the Russian military kept up its effort to take control of Bakhmut.

A top Ukrainian commander accused Moscow of using “scorched earth” tactics.

“The enemy switched to so-called scorched earth tactics from Syria. It is destroying buildings and positions with air strikes and artillery fire,” Colonel General Oleksandr Syrskyi, commander of Ukraine’s ground forces, said of Bakhmut.

The battle for the small and now largely ruined city on the edge of a chunk of Russian-controlled territory in Donetsk has been the bloodiest of the 13-month war as Moscow tries to inject momentum into its campaign after recent setbacks.

Both sides have suffered heavy casualties in the Bakhmut fighting, but Syrskyi said: “The situation is difficult but controllable.” The head of the Moscow-controlled part of Donetsk, Denis Pushilin, said Russian forces now held 75 per cent of the city, though he cautioned it was too early to talk about Bakhmut’s fall.

Moscow’s military was also targeting the city of Avdiivka.

“The Russians have turned Avdiivka into a total ruin,” said Pavlo Kyrylenko, Donetsk’s regional governor, describing an air strike on Monday that destroyed a multi-storey building.

“In total, around 1,800 people remain in Avdiivka, all of whom risk their lives every day.”

In Chasiv Yar, the first major town to Bakhmut’s west, few buildings remain intact and those queuing for food and other aid do not even flinch at the sound of artillery.

“It used to be scarier, but now we have got used to it,” said 50-year-old humanitarian volunteer Maksym. “You don’t even pay attention,” he added, his words nearly drowned out by the sound of explosions.

As the battles ground on, US broadcaster CNN said Ukraine was forced to amend some military plans ahead of its long-anticipated counter-offensive because of the leak of dozens of secret documents.

US officials are trying to trace the source of the leak, reviewing how they share secrets internally and dealing with the diplomatic fallout.

The documents detail topics such as information on the Ukraine conflict, in which Washington has supplied Kyiv with huge amounts of weapons and led international condemnation of Moscow’s invasion.

Asked about the report, Ukrainian presidential aide Mykhailo Podolyak said Kyiv’s strategic plans remained unchanged but that specific tactics were always subject to change.

Some national security experts and US officials have said they suspect the leaker could be American, but have not ruled out pro-Russian actors.

Kremlin spokesman Dmitry Peskov declined to comment on the leak, but said: “There is in fact a tendency to always blame everything on Russia. It is, in general, a disease.”

Hot on the eastern front

A Ukrainian counter-offensive has long been expected after months of attritional warfare in the east.

A Russian winter offensive failed to make much progress, and its troops have made only small advances at huge cost.

The Ukrainian defenders have also taken heavy casualties.

Syrskyi said Moscow was sending in special forces and airborne units to help their attack on Bakhmut as members of Russia’s private mercenary Wagner group, who have spearheaded the Bakhmut assault, were exhausted.

Reuters could not verify the battlefield accounts.

Ukraine’s general staff said Russian forces had made unsuccessful advances on areas west of Bakhmut while shelling many towns and villages, including Bakhmut and Chasiv Yar.

Ukrainian forces repelled 52 enemy attacks, it said.

Donetsk is one of four provinces in eastern and southern Ukraine that Russia declared annexed last year and is seeking to fully occupy in what appears to be a shift in its war aims after failing to overrun the country after its February 2022 invasion.

Control of Bakhmut could allow Russia to directly target Ukrainian defensive lines in Chasiv Yar and open the way for its forces to advance on two bigger cities in the Donetsk region - Kramatorsk and Sloviansk.

Last week, President Volodymyr Zelenskiy said troops could be withdrawn if they ran the risk of being encircled. Kyiv and the West say the now smashed city of Bakhmut has only symbolic importance.

‘Significant’ number of leaks are fake, South Korea states.

South Korea on Tuesday said a “significant portion” of leaked US intelligence documents indicating concerns in Seoul about arms supplies to Ukraine were fake.

The documents are part of a broader leak the Pentagon has described as a “very serious” national security risk. It has also created a diplomatic headache for Washington as they appear to show US spying on close allies including South Korea and Israel.

Some files reportedly show concern among top South Korean national security officials that arms and ammunition manufactured by their country might end up being used in Ukraine — a violation of Seoul’s policy of not selling weapons to nations at war.

In a call on Tuesday, the South Korean defence minister and the US secretary of defence agreed that “a significant number of the documents in question were fabricated”, the presidential office in Seoul said in a statement.

Dozens of photographs of the documents have been circulating on social media platforms and messaging services including Twitter, Telegram and Discord for at least weeks.

The Pentagon has said it is working to determine if the documents are genuine, and that at least one appeared to have been manipulated.

However, US officials reportedly believe many of the documents are real.

The leak has prompted US officials to reassure allies such as South Korea, which has provided non-lethal and humanitarian aid to Ukraine since Russia invaded last year.

But Seoul has a long-standing policy against providing weapons to countries in active conflict, which it says makes it difficult to supply arms directly to Ukraine.

The revelation of the purported Ukraine discussions among top national security officials has sparked criticism in South Korea about the vulnerability of sensitive sites including the presidential office.

But President Yoon Suk Yeol’s office pushed back Tuesday, saying it had “iron-clad security” and that allegations of eavesdropping were “senseless lies”.

Yoon is scheduled to travel to the United States later this month on a state visit.