The most intense fighting has centred on the southeastern Zaporizhia province, around the city of Bakhmut and further west in Ukraine’s eastern Donetsk province, according to a British intelligence assessment on Sunday.

Ukraine is on the offensive in these areas and “made small advances”, it said. Russian forces are conducting “relatively effective defensive operations” in Ukraine’s south.

Serhiy Bratchuk, spokesperson from the regional government in southwestern Odesa province, said Ukrainian forces destroyed a “very significant” ammunition depot near the Russian-occupied port city of Henichesk in nearby Kherson province.

“Our armed forces dealt a good blow in the morning,” Bratchuk said in a video message posted to his Telegram channel.

Western analysts and military officials have cautioned that Ukraine’s counteroffensive to dislodge Russian forces from occupied areas along the 1,000km (620-mile) front line could last a long time.

A Russian-installed official said Ukrainian troops recaptured Piatykhatky, a village in the southern Zaporizhia region, and were entrenching themselves there while coming under fire from Russian artillery.

“The enemy’s ‘wave-like’ offensives yielded results, despite enormous losses,” the official, Vladimir Rogov, said on the Telegram messaging app.

Russia’s defence ministry made no mention of Piatykhatky in its daily update, in which it said its forces had repelled Ukrainian attacks in three sections of the front line. A separate statement from Russia’s Vostok group of forces said Ukraine had failed to take the settlement.

Al Jazeera could not independently verify the battlefield reports.

The Ukrainian military said on Sunday that over the previous 24 hours, Russia carried out 43 air strikes, four missile attacks, and 51 rocket launches.

According to its statement, Russia continues to concentrate its efforts on offensive operations in Ukraine’s industrial east, focusing attacks around Bakhmut, Avdiivka, Marinka, and Lyman in Donetsk province, with 26 combat clashes taking place.

‘No chance,’ says Putin

Ukraine’s President Volodymyr Zelenskyy on Sunday praised Ukrainian forces for their “very effective” repelling of enemy assaults near Avdiivka.

He also described the southern front as “the most brutal” and expressed gratitude to troops fighting there.

Meanwhile, Wagner Group boss Yevgeny Prigozhin said on Sunday that 32,000 former Russian prisoners returned home after the end of their contracts with the mercenary militia fighting in Ukraine.

According to Prigozhin, 83 crimes were committed by those who gained their freedom and returned Russia, which he claimed was “80 times less” than the number committed by those released from prison over the same period without having served with Wagner.

Prigozhin toured Russian prisons to recruit fighters, promising pardons if they survived a half-year tour of front-line duty with Wagner. In an interview last month, Prigozhin said he recruited 50,000 convicts, about 10,000 of whom were killed in Bakhmut.

Russian President Vladimir Putin, who rarely comments on the course of the war, made two unusually detailed interventions last week, in which he derided the Ukrainian push and said Kyiv’s forces had “no chance” despite being newly equipped with Western tanks.

His comments appeared intended to reassure Russians at a crucial juncture, nearly 16 months into the conflict, as Ukraine seeks to break months of virtual stalemate and take back the 18 percent of its territory that remains under Russian control.

Meanwhile, the United Nations said on Sunday that Russia has “so far declined our request to access the areas under its temporary military control” after the destruction of the Nova Kakhovka dam on June 6 in the southern region of Kherson unleashed 18 cubic kilometres (4.3 cubic miles) of water that submerged villages and farmland.

“The UN will continue to engage to seek the necessary access. We urge the Russian authorities to act in accordance with their obligations under international humanitarian law,” said Denise Brown, the UN humanitarian coordinator for Ukraine, in a statement. “Aid cannot be denied to people who need it.”

Zelenskyy accused Russia of deliberately blowing up the dam, calling it a “war crime” and “brutal ecocide”. Moscow has denied causing the blast.