Russia could use phosphorus munitions in Mariupol as the fighting for the besieged Ukrainian city intensified, the UK’s Ministry of Defence has warned.

       In the latest intelligence update, MoD said that white phosphorous has already been used by Russia in the Donetsk region of eastern Ukraine.

       This came amid Ukrainian president Volodymyr Zelensky’s heightened fears of Russia amassing thousands of troops for a renewed offensive on the already-war battered port city.

       White phosphorus is a toxic substance that is used for illumination at night or to create a smokescreen, but when used as a weapon it causes horrific burns.

       The British intelligence said: “Russian shelling has continued in the Donetsk and Luhansk regions, with Ukrainian forces repulsing several assaults resulting in the destruction of Russian tanks, vehicles, and artillery equipment.”

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       It warned that Russia was “greatly risking the risk of further civilian casualties” with “continued reliance on unguided bombs decreases their ability to discriminate when targeting and conducting strikes”.

       Meanwhile, the head of Russia’s republic of Chechnya, Ramzan Kadyrov, has warned of unleashing an offensive not only on Mariupol but also on the capital Kyiv and other Ukrainian cities.

       “There will be an offensive ... not only on Mariupol, but also on other places, cities and villages,” Mr Kadyrov said in a video posted on his Telegram channel. “Luhansk and Donetsk - we will fully liberate in the first place ... and then take Kyiv and all other cities.”

       Mr Zelensky told South Korea’s parliament by videolink that the coming week would be important as suspected “even larger operations in the east of our state”.

       “Russian troops will move to even larger operations in the east of our state. They may use even more missiles against us, even more air bombs. But we are preparing for their actions. We will answer,” he said.

       Graves of civilians killed during Ukraine-Russia conflict are seen next to apartment buildings in the southern port city of Mariupol

       (REUTERS)

       The port city of Mariupol, a strategically important port on the Sea of Azov that is a part of the Black Sea, has been encircled by Russian forces since the beginning of March.

       This map shows the extent of the Russian invasion of Ukraine

       (Press Association Images)

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       The city has been pummelled by endless bombardment from artillery, rockets and missiles as Ukrainian forces said they have been fending off attacks on the city for more than 40 days.

       More than 90 per cent of the city has been reportedly damaged and access to electricity, heating, freshwater, food and medical supplies has been cut off.