The UN Security Council will on Tuesday discuss behind closed doors Russia's claims that Ukraine plans to detonate a "dirty bomb" and blame it on Moscow, diplomats said.
Russia's UN ambassador, Vasily Nebenzya, repeated the claim that Kiev was planning such a provocation in a letter to the council and to UN Secretary-General Antonio Guterres seen by AFP.
The allegation, which came as Russia has faced significant setbacks eight months into its invasion of Ukraine, has been rejected by Kyiv and its Western partners.
Russian Defence Minister Sergei Shoigu made the claim on Sunday in calls with Nato counterparts, alleging that Ukraine planned to detonate a crude bomb that could spew dangerous nuclear, chemical or biological materials.
The United States, France and Britain rejected that in a joint statement on Sunday, suggesting it was a scheme by Moscow to ratchet up the war.
"The world would see through any attempt to use this allegation as a pretext for escalation," their statement said.
In a tweet ahead of the Security Council meeting, Britain's UN mission reiterated its stance.
"Reminder: Ukraine has no nuclear weapon," it said.