Service members of pro-Russian troops inspect streets during Ukraine-Russia conflict in Mariupol, Ukraine. Reuters

Ukraine pleaded for more weapons from the West to help it end the siege of Mariupol and fend off an expected Russian offensive in the east, as more reports emerged of rape and brutality against Ukrainian civilians by Russian forces.

Russia has nearly completed its buildup for a renewed assault on Ukraine's eastern Donetsk and Luhansk regions, Ukraine's defence ministry said. The governor of Luhansk said Russia was moving military vehicles closer to the front lines in the region.

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More than 10,000 civilians dead in Ukraine port city of Mariupol

Ukraine prepares for new Russian assault

Russia is believed to be trying to connect occupied Crimea with Moscow-backed separatist territories Donetsk and Lugansk in Donbas, and has laid siege to the strategically located city, once home to more than 400,000 people.

Ukrainian forces were "surrounded and blocked", tweeted Myhaylo Podolyak, an official from President Volodymyr Zelensky's office.

Ukraine President Volodymyr Zelensky

But on Monday the Ukrainian army insisted that "the defence of Mariupol continues".

"The connection with the units of the defence forces that heroically hold the city is stable and maintained," the Land Forces of Ukraine wrote on Telegram.

In his nightly address, Zelensky made another plea to his allies for more weapons to boost the defence of the city.

"We are not getting as much as we need to end this war sooner. To completely destroy the enemy on our land... in particular, to unblock Mariupol," he said.

He made a similar appeal for military assistance to South Korea's National Assembly earlier in the day, telling lawmakers Russia had "completely destroyed Mariupol and burned it to ashes".

"At least tens of thousands of Mariupol citizens must have been killed," he added.