KYIV, UKRAINE -- Russia and are suffering high numbers of military casualties as Ukraine fights to dislodge the Kremlin's forces from occupied areas in the early stages of its counteroffensive, British officials said Sunday.

Russian losses are probably at their highest level since the peak of the battle for Bakhmut in March, U.K. military officials said in their regular assessment.

According to British intelligence, the most intense fighting has centered on the southeastern Zaporizhzhia province, around Bakhmut and further west in Ukraine's eastern Donetsk province. While the update reported that Ukraine was on the offensive in these areas and had "made small advances," it said that Russian forces were conducting "relatively effective defensive operations" in Ukraine's south.

The Ukrainian military said in a regular update Sunday morning that over the previous 24 hours Russia had carried out 43 airstrikes, four missile strikes and 51 attacks from multiple rocket launchers. According to the statement by the General Staff, 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.

Donetsk regional Gov. Pavlo Kyrylenko said that two civilians were killed, with a further three wounded in the past day.

Ukrainian officials said Russian forces also launched airstrikes on other regions of the east and south of the country.

One civilian was killed and four more wounded in Kherson province as a result of Russia's attacks, said regional Gov. Oleksandr Prokudin, while Zaporizhzhia regional Gov. Yurii Malashko said one person was wounded in Russian attacks that hit 20 settlements in the province.

Vladimir Rogov, an official with the Moscow-appointed administration in the partially occupied Zaporizhzhia region, said Sunday that Ukrainian forces had taken control of the village of Piatykhatky on the Zaporizhzhia battlefront.

Serhiy Bratchuk, spokesperson of the regional government in the southwestern Odessa 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 on Sunday morning, posted to his Telegram channel.

Western analysts and military officials have cautioned that Ukraine's counteroffensive to dislodge the Kremlin's forces from occupied areas, using Western-supplied advanced weapons in attacks along the 1,000-kilometre (600-mile) front line, could last a long time.

A group of African leaders carried out a self-styled "peace mission" to both Ukraine and Russia in recent days to try to help end their nearly 16-month-old war, but the visit ended on Saturday with no immediate signs of progress.

In other developments:

-- Volodymyr Artyukh, the governor of Ukraine's northern Sumy region, which borders Russia, said a father and his son were killed by Russian shelling of the village of Bilopilya. Across the border, Ukrainian shelling hit three villages in Russia's Kursk region, said its governor Roman Starovoit.

-- The death toll from flooding following the destruction of the Kakhovka dam has risen to 16 in Ukrainian-held territory, Ukraine's interior ministry said late Saturday, while Russian officials said 29 people died in territories controlled by Moscow.

Massive flooding from the destruction of the dam on June 6 devastated towns along the lower Dnipro River in Kherson province, a front line in the war. Russia and Ukraine accuse each other of causing the breach.

-- As the deadline for all Russian volunteer formations to sign contracts with Russia's Defense Ministry approaches, widely seen as targeting Russia's Wagner mercenary group, Wagner leader and regular Kremlin critic Yevgeny Prigozhin said Sunday that 32,000 former prisoners had returned home after the end of their contracts with Wagner in Ukraine.

According to Prigozhin, 83 crimes were committed by those who had returned home, 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 had recruited 50,000 convicts, about 10,000 of whom were killed in Bakhmut.