Russia is believed to be trying to connect occupied Crimea with Moscow-backed separatist territories Donetsk and Lugansk in Donbas

Kramatorsk (Ukraine) (AFP) - Russian troops aimed to take control of the city of Mariupol on Tuesday, part of an anticipated massive onslaught across eastern Ukraine, as defending forces tried desperately to hold them back.

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.

“It is likely that in the future the enemy will try to take control of the city of Mariupol, capture Popasna and launch an offensive in the direction of Kurakhove in order to reach the administrative borders of Donetsk region,” the General Staff of the Armed Forces of Ukraine said on Facebook.

The Russian defence ministry said it army had thwarted an attempt to break the siege with “airstrikes and artillery fire” at a factory in a northern district of the city.

But 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.

Map locating advances by Russian forces in Mariupol as of April 10 at 1900 GMT

In his nightly address, President Volodymyr 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” killing “at least tens of thousands of people”.

- Chemical weapons allegations -

Late Monday, Britain said it was trying to verify reports that Russia had also used chemical weapons in the city.

Western officials have previously expressed concerns that as the conflict drags into its seventh week, Russia could resort to such extreme measures.

Ukrainian lawmaker Ivanna Klympush said Russia had used an “unknown substance” and that people were suffering from respiratory failure.

Russian soldiers have been patrolled the streets in Volnovakha in the self-proclaimed Donetsk People's Republic

But deputy defence minister Ganna Maliar said the purported chemical attack was more likely phosphorous munitions.

“Officials conclusions will be made later,” she told Ukrainian television.

Eduard Basurin, a senior official in the separatist area of Donetsk in eastern Ukraine, has spoken of the possibility of such arms being used in Mariupol but insisted on Tuesday that “no chemical weapons have been used” in the city.

Elsewhere in the east, heavy bombardment continued as civilians were urged to flee ahead of an expected Russian troop surge in the region.

Russian forces are reinforcing around the Donbas region, notably near the town of Izyum, but have not yet launched a full offensive, Pentagon officials said Monday.

They reported a Russian convoy had been observed heading for Izyum, an hour’s drive north of Kramatorsk, saying it appeared to be a mix of personnel-carriers, armoured vehicles and possible artillery.

President Vladimir Putin insisted that Russia’s own security was at stake in Donbas, after talks at the Russian spaceport in Vostochny with Belarusian President Alexander Lukashenko.

“What we are doing is helping people – rescuing them on the one hand and on the other taking measures to assure Russia’s security,” he said, according to Russian news agencies.

The body of a civilian was exhumed from a shallow grave near in the village of Andriivka in the Kyiv region

Ukraine’s defence ministry said it believed a major assault would happen soon.

“We don’t know precisely when, but the preparation is almost over,” spokesman Oleksandr Motuzyanyk told a briefing on Monday.

- ‘Logic of war’ -

Such signs of a build-up in Donbas suggest hopes of an imminent diplomatic solution remain slim.

After a meeting with Putin on Monday, Austrian Chancellor Karl Nehammer said he was “rather pessimistic” of such efforts succeeding as Putin had “massively entered into a logic of war”.

Ukraine’s allies are trying instead to increase economic and diplomatic pressure on Moscow – but EU foreign ministers’ discussions on a sixth round of sanctions on Monday came up dry.

“Nothing is off the table, including sanctions on oil and gas,” said Josep Borrell, the European Union’s top diplomat. “But today, no decision was taken.”

Residents took shelter from the shelling in Kharkiv

In an effort to shore up wider support for Kyiv, US President Joe Biden held virtual talks with Indian Prime Minister Narendra Modi just weeks after saying New Delhi had been “shaky” in its response to the invasion.

Meanwhile the toll on towns previously occupied by Russian forces during their month-long offensive to take Kyiv was still coming to light.

AFP saw the bodies of three men in civilian clothes exhumed from gardens in Andriivka, 33 kilometres (20 miles) west of the capital as relatives gathered to learn the fate of their kin.

The UN Security Council – which on Monday held a session on the plight of women and children in Ukraine – will hold another meeting next week on the humanitarian situation there, in a bid to keep pressure on Russia despite its veto power over the body, diplomats said.

- ‘Rape and sexual violence’ -

At Monday’s UNSC meeting, officials called for an investigation into violence against women during the conflict.

The toll on towns previously occupied by Russian forces during their month-long offensive to take Kyiv is still coming to light

“This war must stop. Now,” Sima Bahous, director of the UN women’s agency, told the Council.

“We are increasingly hearing of rape and sexual violence. These allegations must be independently investigated to ensure justice and accountability.”

More than 4.5 million Ukrainian refugees have now fled their country, the United Nations refugee agency said – 90 percent of them women and children.

The war has displaced more than 10 million people overall.

One of those was Tatyana Kaftan, just weeks away from giving birth to her first child, who spoke to AFP at an aid distribution point in the western city of Lviv.

Her husband, who is waiting to be called up to the army, stood by her side.

“We left everything at home,” said the 35-year-old travel agent, who drove with her husband all the way from Mykolaiv to escape Russian shelling.

“We have nothing.”