U.N. investigators say repression in Belarus, Russia’s ally, could amount to crimes against humanity.

Britain on Wednesday defended its decision to supply Ukraine with weapons made with depleted uranium, a day after President Vladimir V. Putin of Russia falsely claimed the material had a “nuclear component.”

Britain’s government has confirmed that it would provide Ukraine with armor-piercing shells that contain depleted uranium, alongside its Challenger 2 tanks, which use them. Depleted uranium is a standard component in conventional anti-armor weapons that NATO countries have used for decades, and Britain said in a statement that the ammunition it was providing had nothing to do with nuclear weapons.

The density of depleted uranium makes it an effective material for piercing heavy armor on the battlefield, and is used by many militaries. Among them are Russia’s, which upgraded its main battle tank to add the ability to fire depleted uranium shells, the Tass state news agency reported in 2018.

James Cleverly, Britain’s foreign secretary, told reporters on Wednesday that there was “no nuclear escalation,” adding, “The only country in the world that is talking about nuclear issues is Russia.”

Uranium, a heavy metal, must be enriched to be used for nuclear purposes. Depleted uranium, which is about two and a half times denser than steel, is a byproduct of that enrichment, still radioactive but at a much lower level.

Mr. Putin’s false assertion came in a statement on Tuesday during his summit with China’s leader, Xi Jinping, who U.S. officials believe has been urging Russia not to use nuclear weapons in Ukraine.

Depleted uranium has been used by militaries as far back as the 1990 Gulf War, so “this is nothing new and nothing unusual,” said Stuart Crawford, a defense analyst and former army officer in Britain. Mr. Crawford said that Russia uses depleted uranium in some of its ammunition, including 125-millimeter tank rounds.

It is certainly not a “nuclear component” as Mr. Putin described it, he said.

“Saying this ups the ante or escalates the conflict because of the nuclear aspect is just nonsense,” Mr. Crawford said.

Questions have long followed the use of depleted uranium in some munitions and armor, as outside groups have raised environmental and safety concerns. A 2022 report from the United Nations Environment Program identified depleted uranium as a risk in the war in Ukraine, saying that while it does not release radiation that can penetrate healthy skin, it “does have the potential to cause radiation damage if inhaled or ingested,” which can happen when the material is pulverized on impact.

The Pentagon has also deemed depleted uranium safe, though after the U.S. military used it in Iraq, some activists and others connected it to birth defects and cancers. Numerous studies have been conducted on a possible link, without firm conclusions.

In 2013, Britain’s Ministry of Defense downplayed any health or environmental risks related to the use of depleted uranium. In a paper, it said that while the dust released on impact can sometimes be a health hazard, “all the research to date indicates that these circumstances are extremely unlikely to occur, and, if they do, will only affect very small groups who will be at much greater risk from the other hazards associated with armed conflict.”

The Pentagon spokesman, Brig. Gen. Patrick S. Ryder, said in a briefing on Tuesday that, to his knowledge, the United States has not provided Ukraine with any ammunition that includes depleted uranium.

Mr. Putin’s comments did not appear to be related to environmental or heath risks, but instead accused the West of escalating the war by sending weapons with depleted uranium and said Russia “will have to respond accordingly.” That appeared to be a veiled threat to wield Moscow’s nuclear arsenal in Ukraine, as Mr. Putin has warned of at times during the war.

U.S. officials have said they have seen no effort by Russia to move or employ its nuclear weapons and believe the risk of their use is low, though worries linger.