Kyiv: Fierce fighting between Russian and Ukrainian forces continued on Thursday in Severodonetsk.

"The situation is consistently difficult. Our defenders are holding the line of defence, levelling the line of defence," Serhiy Hayday, head of Ukraine's eastern Luhansk region military administration, said on national television, reported CNN.

"The fiercest fighting continues in Severodonetsk," Hayday said. The city has seen intense battles in recent days. Hayday accused the Russians of using "lies and propaganda" in claiming victory in the Severodonetsk.

The key eastern Ukrainian city of Severodonetsk is now mostly controlled by Russian forces, according to local officials, after what they described as a "difficult" Thursday night.

Hayday said there are no direct battles in the neighbouring city of Lysychansk, but he accused Russian forces of heavily shelling the area.

If Russian troops take control of Lysychansk and Severodonetsk, it would place all of the Luhansk region under Moscow's control.

The Russians had already reported that they had taken the city, a Russian official said, and added that some forces had withdrawn part of their units, reported CNN.

However, Oleksandr Striuk, head of Severodonetsk's military administration, said that there is "constant street fighting."

"The humanitarian situation in the city is critical. The bridge is under fire, so it is impossible to deliver goods. There is no water supply," Striuk said.

"The Ukrainian Armed Forces control approximately one-third of the city now," he added, saying it will be "very difficult to liberate Severodonetsk (if it falls)."

Ukraine's President Volodymyr Zelenskyy has said the fate of the whole Donbas region is being decided in the fight for Severodonetsk.

Meanwhile, there are reports that three men -- two Britons and a Moroccan -- were sentenced to death by a pro-Russian court in the self-proclaimed Donetsk People's Republic.

They served as foreign fighters for the Ukrainian military and were captured by Russian forces in mid-April in Mariupol, reported CNN.

In the early hours of February 24, Russia launched a special military operation in Ukraine claiming that Donetsk and Luhansk People's Republics (DPR and LPR) had appealed for help in defending themselves against the Kyiv forces.

Russia said that the aim of its special operation was to "demilitarize" and "denazify" Ukraine and that only military infrastructure was being targeted. Moscow has also stressed that it has no plans to occupy Ukraine.