Kyiv: Ukraine President Volodymyr Zelenskyy urged the West to stop playing around with Russia and impose tougher sanctions on Moscow to end its "senseless war" in Ukraine, adding his country would remain independent, the only question was at what price.

Zelenskyy's criticism of the West has mounted in recent days as the European Union moves slowly towards a possible Russian oil embargo and as thousands of Russian forces try to encircle two key eastern cities of Sievierodonetsk and Lysychansk.

Three months into its invasion of Ukraine, Russia has abandoned its assault on the capital Kyiv and is trying to consolidate control of the industrial eastern Donbas region, where it has backed a separatist revolt since 2014.

Western military analysts see the battle for Sievierodonetsk and Lysychansk as a potential turning point in the war after a shift in momentum towards Russia following the surrender of Ukraine's garrison in Mariupol last week.

"Ukraine will always be an independent state and it won't be broken. The only question is what price our people will have to pay for their freedom, and what price Russia will pay for this senseless war against us," said Zelenskyy in a late-night address on Thursday.

"The catastrophic unfolding events could be still stopped if the world treated the situation in Ukraine as if it were facing the same situation, if the powers that be did not play around with Russia but really pressed to end the war."

Zelenskyy complained about disagreements within the EU on more sanctions against Russia and asked why some nations were being allowed to block the plan.

The EU is discussing a sixth round of punitive measures,including an embargo on Russian oil imports. Such a move requires unanimity but Hungary opposes the idea for now on the grounds its economy would suffer too much.

"How many more weeks will the European Union try to agree on a sixth package?" Zelenskyy asked, noting Russia was receiving one billion euros a day from the 27-nation bloc for energy supplies.

"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."

Zelenskyy's comments mark the second day in a row that he has sharpened his criticism of the world's approach to the war.

On Wednesday, he savaged suggestions that Kyiv make concessions to bring peace, saying the idea smacked of attempts to appease Nazi Germany in 1938.

Advancing Russian troops

Russian forces attacked from three sides to try to encircle Ukrainian forces in Sievierodonetsk and Lysychansk on Thursday, said Ukraine's military. If the two cities straddling the Siverskiy Donets river fall, nearly all of the Donbas province of Luhansk would be under Russian control.

Luhansk governor Serhiy Gaidai said around 50 Russian soldiers had reached the highway and "managed to gain a foothold", even setting up a checkpoint.

"The checkpoint was broken, they were thrown back ... the Russian army does not control the route now, but they are shelling it," he said. It was possible Ukrainian troops would leave "one settlement, maybe two. We need to win the war, not the battle," he said.

"It is clear that our boys are slowly retreating to more fortified positions - we need to hold back this horde."

Ukrainian interior ministry adviser Vadym Denisenko told a briefing 25 Russian battalions were attempting to surround the Ukrainian forces.

Reuters journalists in Russian-held territory further south saw proof of Moscow's advance in Svitlodarsk, where Ukrainian forces withdrew earlier this week.

The town is now firmly under control of pro-Russian fighters, who have occupied the local government building and hung a Soviet hammer and sickle flag at the door.

Reuters drone footage of the nearby abandoned battlefield showed craters pockmarking a green field surrounded by wrecked buildings. Pro-Russian fighters were milling about in trenches.

The Donbas advance has been backed by massive artillery bombardment. Ukraine's military said 50 towns in the Donetsk and Luhansk provinces came under shelling on Thursday.

The head of Ukraine's armed forces, Valeriy Zaluzhny, called on Telegram for more Western arms, particularly "weapons that will allow us to hit the enemy at a big distance".

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

Danger of escalation

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

Washington is even considering providing Kyiv with a rocket system that can have a range of hundreds of kilometres, and has held discussions with Kyiv about the danger of escalation if it strikes deep inside Russia, US and diplomatic officials told Reuters.

"We have concerns about escalation and yet still do not want to put geographic limits or tie their hands too much with the stuff we're giving them," said one US official, speaking on condition of anonymity.

Russia calls its actions in Ukraine a "special operation" to disarm Ukraine and protect it from fascists. Ukraine and the West say the fascist allegation is baseless and that the war is an unprovoked act of aggression.

Kremlin spokesperson Dmitry Peskov said Moscow expects Ukraine to accept its demands at any future peace talks. It wants Kyiv to recognise Russian sovereignty over the Crimea peninsula Moscow seized in 2014, and the independence of separatist-claimed territory.