Russian forces in a “frenzied push” seized half of the eastern Ukrainian city of Sievierodonetsk as Ukrainian forces held against an out all-out assault.

Both sides said Russian forces now controlled between a third and half of the city.

Local officials say the evacuation of civilians out of Severodonetsk has been stopped due to Russian shelling.

The regional governor, Serhiy Haidai, told the BBC earlier that up to 15,000 civilians may still be trapped in the city.

Jan Egeland, the secretary general of the Norwegian Refugee Council aid agency which has long operated out of the city, told Reuters that he was "horrified" by its destruction.

"[Thousands of civilians] remain caught in the crossfire in the city, without sufficient access to water, food, medicine or electricity," he said.

"The near-constant bombardment is forcing civilians to seek refuge in bomb shelters and basements, with only few precious opportunities for those trying to escape."

Moscow has drained manpower and firepower from across the rest of the front to concentrate on Sievierodonetsk, hoping a massive offensive on the small industrial city will deliver something Russia can call a victory in one of its stated aims in the east.

Efforts to capture the Donbas before more Western arms arrive to bolster Ukraine’s defense. Moscow-backed separatists already held territory in the region and have been fighting Ukrainian troops for eight years.

"The front line has cut [Severodonetsk] into two halves," city head Oleksandr Stryuk told Ukrainian TV. Luhansk regional Governor Serhiy Haidai described it as "a grave situation there".

The EU on Monday agreed its toughest sanctions against Russia since the war began, for the first time targeting Russian sales of oil, by far Moscow's main source of income.

The EU will now ban import of Russian oil by sea. Officials said that would halt two-thirds of Russia's oil exports to Europe at once, and 90% by the end of this year as Germany and Poland also phase out imports by pipeline.

Hungary, which relies on Russian oil through a huge Soviet-era pipeline, secured an exemption, though EU officials said they expected this would be "temporary".

Ukraine says the sanctions are taking too long and are still too full of holes to stop Russia: "If you ask me, I would say far too slow, far too late and definitely not enough," said Ihor Zhovkva, deputy head of President Volodymyr Zelenskiy's office.
-AP/Reuters/BBC