Foreign Minister Sergei Lavrov spoke as Moscow's soldiers smashed Ukrainian defences close to Kharkiv, the country's second largest city.
The attack has forced more than 6,000 Ukrainians to flee their homes to escape the enemy advance.
Lavrov warned that Russia was ready for direct conflict with Western troops if they were sent to defend Ukrainian soil.
He said of the choice facing Nato powers: "It's their right. If they want it to be on the battlefield, it will be on the battlefield."
He spoke after Sweden's Prime Minister Ulf Kristersson said he would host Western nuclear weapons should war break out.
Mr Kristersson said: "Should the very worst happen, the democratic countries in our part of the world must be able to defend themselves.
Destroyer
"Our entire Nato membership and Swedish defence aim is to prevent that situation from occurring.
"If Ukraine had been a member of Nato, they would not have been attacked by Russia."
Western allies were surprised after Vladimir Putin sacked his veteran defence minister Sergei Shoigu and replaced him with deputy prime minister Andrei Belousov.
This story is from the May 14, 2024 edition of Daily Express.
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This story is from the May 14, 2024 edition of Daily Express.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 8,500+ magazines and newspapers.
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