United States President Joe Biden on Tuesday said that Russia will be making an “incredibly serious mistake” if it were to use a tactical nuclear weapon against Ukraine, reported CNN.

Biden’s comments came after Moscow’s defence minister had claimed on Monday that Ukraine plans to use a radioactive “dirty bomb”, an explosive laced with radioactive material, on Russia. However, Russia had not provided any evidence to support its claims.

Ukrainian President Volodymyr Zelenskyy had dismissed such claims by Russia.

“When the Russian Minister of Defense organises a phone carousel and calls foreign ministers with stories about the so-called ‘dirty’ nuclear bomb, everyone understands everything well,” Zelenskyy wrote on Facebook. “Wherever Russia has brought death and degradation, we are restoring normal life.”

The Ukrainian president also said that if Russia is preparing to raise the stakes of the war it must be prevented.

Meanwhile, the US has said that it is monitoring the situation regarding any potential preparations for use of a dirty bomb in Ukraine, reported CNN.

“If an actor wanted to do a dirty bomb attack, a lot of our ability to detect would be determined by a range of factors, including the length of time that the perpetrator was going to prepare for or the communications that would be involved in doing that, and size and location,” US strategic communications coordinator for the National Security Council John Kirby had said on Monday.