Russia-backed rebels in eastern Ukraine on Friday claimed to have taken full control of the important battlefield town of Lyman, a town in the Donetsk region, and Ukraine appeared to concede it, as Moscow presses its biggest advance in weeks.

The military of the self-proclaimed Donetsk republic said on Telegram that rebel forces, supported by Russian troops, as of Friday "have liberated and taken full control of 220 settlements, including Lyman."

There has been no confirmation yet from Ukrainian officials. Lyman, the site of a key railway hub, has been a major front line as Russian forces press down from the north, one of three directions from which they have been attacking Ukraine's industrial Donbass region. The pro-Russian Donetsk People's Republic separatists said they were now in full control of it.

Oleksiy Arestovych, an adviser to Ukrainian President Volodymyr Zelenskyy, appeared to confirm the fall of Lyman in an interview overnight and said the battle there showed that Moscow was improving its tactics.

"According to unverified data, we lost the town of Lyman. The Russian army – this must be verified – captured it," Arestovych said in a video posted on social media.

According to official Ukrainian figures, around 1,500 people have been killed in the particularly hard-fought eastern Ukrainian city of Severodonetsk since the beginning of the war.

Among them were soldiers as well as civilians, the head of the local military administration, Oleksandr Stryuk, said Friday.

Many people have also fled. Of the former 130,000 inhabitants, only about a 10th is still there.

The governor of Luhansk, Serhii Haidai, also reported that four people had been killed by Russian shelling on the residential areas of Severodonetsk the day before.

More than three months after the start of the Russian war, the large city of Severodonetsk is one of the last parts of Luhansk still controlled by the Ukrainian army. Not far from the city limits, however, there is already fierce fighting.

Russian troops are attempting to gain full control over Ukraine's Luhansk and Donetsk regions, but their efforts have been unsuccessful so far, the Ukrainian General Staff said Thursday.

Observers fear that Ukrainian brigades in Severodonetsk could be encircled by Russian and pro-Russian military forces.

After being driven back from the capital Kyiv in March and from the outskirts of the second biggest city Kharkiv earlier this month, Russian forces are staging their strongest advance in weeks in the eastern Donbass region.

Western military analysts say the battle there could prove decisive, depending on whether Russian forces can sustain the advance or run out of momentum.

Further east, Russian forces have been trying to encircle Ukrainian troops in the cities of Severodonetsk and Lyshchansk, after breaking through Ukrainian lines further south in the city of Popasna last week.

Popasna, reached by Reuters journalists in Russian-held territory on Thursday, was a blasted wasteland of burnt-out highrise apartments and shattered municipal buildings. Russian tanks and other military vehicles tore through the rubble-strewn streets kicking up dust with their treads, and low-flying attack helicopters thundered overhead. The bloated body of a dead man in uniform lay in a courtyard.

'What price'

In an overnight address, Zelenskyy criticized the European Union for taking too long to ban Russian energy imports, saying the bloc was sending Moscow a billion euros a day, which was funding the Kremlin's war effort. He said some countries were blocking efforts to agree on new sanctions, an apparent reference to Hungary, which has objected to an EU ban on Russian oil.

"Pressure on Russia is literally a matter of saving lives. Every day of procrastination, weakness, various disputes or proposals to 'pacify' the aggressor at the expense of the victim merely means more Ukrainians being killed," he said.

Western countries led by the United States have provided Ukraine with long-range weaponry, including M777 howitzers and Harpoon anti-ship missiles from Denmark.

Ukraine says it wants long-range ground weapons, especially rocket launchers, that can help it win an artillery battle against Russian forces in the east.

Meanwhile, Zelenskyy on Thursday accused Russia of carrying out "an obvious policy of genocide" in his country's eastern Donbass region. Moscow's offensive in Donbass could end up leaving the region "uninhabited," he said, accusing the Russians of wanting to reduce its cities to ashes.

"All this, including the deportation of our people and the mass killings of civilians, is an obvious policy of genocide pursued by Russia," he said in his daily televised address.

Russian Foreign Minister Sergei Lavrov warned that any supplies of weapons that could reach Russian territory would be "a serious step toward unacceptable escalation."