Russia's top diplomat has warned against provoking a third world war, adding that the threat of a nuclear conflict "should not be underestimated".
Foreign Minister Sergei Lavrov said NATO members are "pouring oil on the fire" by supporting Ukraine, according to a transcript on the Russian Foreign Ministry's website.
Mr Lavrov accused NATO of effectively having "entered into a war with Russia through proxies, and is arming those proxies".
"Everyone is reciting incantations that in no case can we allow World War Three," he said in a Russian television interview.
Mr Lavrov said he would not want to see risks of a nuclear confrontation "artificially inflated now, when the risks are rather significant".
"The danger is serious. It is real. It should not be underestimated," he said.
Ukraine's Foreign Minister Dmytro Kuleba said on Twitter that Mr Lavrov's comments underscore Ukraine's need for Western help.
He wrote: "Russia loses [its] last hope to scare the world off supporting Ukraine.
"Thus the talk of a 'real' danger of WWIII. This only means Moscow senses defeat in Ukraine."
Meanwhile, the UK Ministry of Defence (MOD) said Russian forces have taken the Ukrainian city of Kreminna in the Luhansk region after days of street-to-street fighting.
In a tweet, the MOD said: "The city of Kreminna has reportedly fallen and heavy fighting is reported south of Izium as Russian forces attempt to advance towards the cities of Sloviansk and Kramatorsk from the north and east."
The US has been rushing more weapons to Ukraine and its Secretary of State and Secretary of Defence said that such assistance from allies is making a difference in the two-month-old war.
After meeting Ukrainian President Volodymyr Zelensky in Ukraine's capital Kyiv during the weekend, Secretary of State Antony Blinken said: "Russia is failing. Ukraine is succeeding."
Watch: Why Vladimir Putin's long-term end game is unclear.
Mr Blinken said Washington had approved a $165m (£130m) sale of ammunition and will also provide more than $300m (£235m) to buy more supplies.
US Defense Secretary Lloyd Austin went further, saying the United States wants to see Ukraine remain a sovereign, democratic country, and to see Russia "weakened" to the extent that it cannot repeat its invasion of Ukraine.
Mr Lavrov has said Russia has "a feeling that the West wants Ukraine to continue to fight and, as it seems to them, wear out, exhaust the Russian army and the Russian military industrial war complex. This is an illusion".
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