Russia's President Vladimir Putin repeats claims made by several Russian officials that Ukraine plans to deploy a "dirty bomb" during Moscow's current military operation in the ex-Soviet republic.
"We are aware of Ukraine's plans to use a dirty bomb," Russia's Interfax news agency cited the head of state as telling a meeting of the intelligence chiefs of several former Soviet countries in Moscow on Wednesday.
Putin added that the risk of conflict in the world and the region was high and that security had to be heightened around key infrastructural sites.
Also on Wednesday, the chief executive oversaw exercises featuring Russia's strategic nuclear forces.
"The tasks envisaged during the training of the strategic deterrence forces were completed in full, all missiles reached their targets," a Kremlin statement said.
Defense Minister Sergei Shoigu told the Russian president that the exercises were practicing "delivering a massive nuclear strike by strategic offensive forces in response to an enemy nuclear strike."
The country's Chief of Staff Valery Gerasimov told Putin the exercise involved intercontinental ballistic missiles, submarines, and Tupolev strategic bomber planes.
Throughout recent weeks, Russian officials have repeatedly accused Ukraine of planning to use the bomb.
Dirty bombs, which are also known as Radiological Dispersal Devices (RDD), are not as potent as nuclear weapons, but can disperse radioactive materials across the targeted areas upon explosion.
Most recently, Russia's UN Ambassador Vassily Nebenzia raised the alert in a letter to United Nations Secretary-General Antonio Guterres and the world body's Security Council on Monday.
He said Ukraine's pending plans to deploy the bomb during the war, amounted to an act of "nuclear terrorism," urging the UN to help avert the prospect.
"We urge the Western countries to exert their influence on the regime in Kiev to abandon its dangerous plans threatening international peace and security," he wrote, adding, "We call on the secretary-general of the United Nations to do everything in his power to prevent this heinous crime from happening."
Ukrainian President Volodymyr Zelensky has responded to Russia's "dirty bomb" allegations by reciprocally accusing Moscow of planning such an attack so it can blame it on Kiev.
Ukraine-allied Western countries have also rejected Russia's allegation, claiming that Moscow is trying to enable the escalation of the conflict.
The developments come amid an ongoing Russian "special military operation" in Ukraine, which Moscow initiated in late February.
The Kremlin says it launched the operation in order to defend the pro-Russian population in the eastern Ukrainian regions of Donetsk and Luhansk against persecution by Kiev.
Back in 2014, the two republics broke away from Ukraine, refusing to recognize a Western-backed Ukrainian government there that had overthrown a democratically-elected Russia-friendly administration.
On Tuesday, US President Joe Biden warned Russia against using a tactical nuclear weapon in Ukraine as Moscow told a closed UN Security Council session that Washington or Kiev may carry out a false flag operation in the country to frame Russia.
“Russia would be making an incredibly serious mistake for it to use a tactical nuclear weapon,” Biden told reporters. “I’m not guaranteeing you that it’s a false flag operation yet. I don’t know. But it would be a serious, serious mistake.”
Russia on Tuesday voiced its concerns to the UN Security Council during a closed-door meeting of the 15-member body.
"We're quite satisfied because we raised the awareness," Russia's Deputy US Ambassador Dmitry Polyanskiy told reporters. "I don't mind people saying that Russia is crying wolf if this doesn't happen because this is a terrible, terrible disaster that threatens potentially the whole of the Earth."
Ukraine has denied any attempt to use such a weapon.