Mr Shoigu spoke of “possible Ukrainian provocations involving a ‘dirty bomb’” — an explosive device that spreads radioactive contamination, the Russian Defence Ministry said.
Mr Wallace rejected the charge and warned Moscow not to try to use it as a “pretext”to intensify the conflict.
“Minister Shoigu alleged that Ukraine was planning actions facilitated by western countries, including the UK, to escalate the conflict in Ukraine," the UK Ministry of Defence said.
“The defence secretary refuted these claims and cautioned that such allegations should not be used as a pretext for greater escalation.”
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The Russian authorities have repeatedly made allegations that Ukraine could detonate a dirty bomb in a “false flag” attack and blame it on Moscow.
The Ukrainian authorities have accused the Kremlin of planning such an attack.
Ukraine’s presidential adviser Mykhailo Podolyak dismissed Mr Shoigu’s claims as an “absolute and quite predictable absurdity from those who believe that they blatantly lie and make people believe in that”.
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The US also rejected Mr Shoigu’s “transparently false allegations,” White House National Security Council spokeswoman Adrienne Watson said.
“The world would see through any attempt to use this allegation as a pretext for escalation,” Ms Watson said.
In his televised address on Sunday evening, Ukrainian President Volodymyr Zelenskyy said Moscow could be setting the stage to use a radioactive device on Ukrainian soil.
“If Russia calls and says that Ukraine is allegedly preparing something, it means only one thing: that Russia has already prepared all of it,” Mr Zelenskyy said.
The mention of the dirty bomb threat in Mr Shoigu’s calls seemed to indicate the threat of such an attack has risen to an unprecedented level.
The French Ministry of the Armed Forces said Mr Shoigu told French Defence Minister Sebastien Lecornu that the situation in Ukraine was rapidly worsening and “trending towards uncontrollable escalation".