• Western officials and strategists say that there are good reasons to fear Moscow using unconventional and outlawed weapons.
• President Joe Biden warned Friday that there would be a "severe price" to pay if Russia used chemical weapons in Ukraine.
• NATO Secretary-General Jens Stoltenberg said Sunday that such a move would be a war crime.

There are increasing concerns that Russia could be prepared to use chemical weapons to attack Ukraine, with Western officials and strategists warning the threat posed by Moscow and Russian President Vladimir Putin in this regard is credible and serious.

In the last week, Russia itself has accused Ukraine of operating chemical and biological weapons laboratories backed by the U.S. The claims were roundly rebuffed by Ukrainian and Western officials, with the U.S. describing them as "outright lies." But they have caused alarm nonetheless, with many officials seeing them as Russia inventing and building a false narrative and pretext for using its own chemical weapons against Ukraine, a prospect described as "horrific" by the U.S.

"Russia has a track record of accusing the West of the very crimes that Russia itself is perpetrating. These tactics are an obvious ploy by Russia to try to justify further premeditated, unprovoked, and unjustified attacks on Ukraine," State Department Spokesperson Ned Price said in a statement last week.

"The United States does not own or operate any chemical or biological laboratories in Ukraine ... It is Russia that has active chemical and biological weapons programs and is in violation of the Chemical Weapons Convention and Biological Weapons Convention," he added.

President Joe Biden warned Friday that there would be a "severe price" to pay if Russia used chemical weapons in Ukraine and NATO Secretary-General Jens Stoltenberg said Sunday that such a move would be a war crime.

"Now that these false claims have been made, we must remain vigilant because it is possible that Russia itself could plan chemical weapons operations under this fabrication of lies," Stoltenberg told the German newspaper Welt am Sonntag.

CNBC has contacted Russia's foreign ministry for a response to the U.S. and NATO's comments.

'Game changer'

While the West has been united in its condemnation of Russia's invasion of Ukraine, with the U.K. describing Putin's regime as "barbaric," just how far the U.S. and its NATO allies are willing to go to support Ukraine, and stop Russia, is a moot point. NATO has repeatedly ruled out any kind of military support, such as a no-fly zone pleaded for by Ukraine, that could lead it into a direct confrontation with nuclear power Russia.

But Poland's President Andrzej Duda said in an interview Sunday that the use of chemical weapons in Ukraine by Russia could change the West's calculus over the conflict.

"Of course, everybody hopes that he would not dare do that but ... if he uses any weapons of mass destruction then this will be a game changer in the whole thing," he told the BBC's Sophie Raworth Sunday, adding that NATO would have to "think seriously what to do because then it starts to be dangerous not only for Europe … but the whole world."

With his almost internationally condemned invasion of Ukraine, which began on Feb. 24, Putin is seen as an increasingly unpredictable leader. With Russia facing far more resistance than it expected to face in Ukraine, and appearing to prepare to attack the capital Kyiv, there are fears that Putin could resort to using unconventional — and outlawed — weapons.

Duda said that Putin had already lost the war politically, and was losing it militarily, and that made the Russian leader dangerous: "If you're asking me whether Putin can use chemical weapons, I think Putin can use anything right now, especially when he's in this difficult situation," he told the BBC.

While fears are heightened that Russia could resort to using chemical weapons in Ukraine, it's important to remember that there is nothing to suggest their use is imminent.

On Friday, Reuters published a briefing by unnamed Western officials who noted that Russia might use chemical weapons in Ukraine in a "false flag" attack to provide a retrospective justification for its invasion, but there is nothing to suggest a broader use of such weapons in the war.

In the Reuters report, the officials said that "clearly, whilst the Russians are highly likely to have a chemical weapons capability, there is nothing to suggest that they intend to use [them] at this point in a major escalation of the current conflict."

Nonetheless, Russia has been accused of using chemical weapons before, both on individuals seen as outspoken critics of Putin, and on a wider level was allegedly complicit in their use in the Syrian civil war.

Russia's reputation

A chemical weapon is defined by the Organisation for the Prohibition of Chemical Weapons as a chemical used to cause intentional death or harm through its toxic properties.

The OPCW's mission is to implement the provisions of the Chemical Weapons Convention, an arms control treaty signed by 193 countries (including Russia) in 1997 which prohibits the production and use of chemical weapons. It also saw signatories commit to destroying chemical weapons production facilities and stockpiles of such weapons.

Putin said in late 2017 that Russia had completed the destruction of its last chemical weapons (and he chided the U.S. for not yet doing so) but the poisoning of former Russian spy (and double agent) Sergei Skripal and his daughter Yulia in the U.K. in 2018 with a Novichok nerve agent (developed by the Soviet Union) and the poisoning of Putin critic and opposition politician Alexei Navalny in 2020 have suggested Russia has maintained an illicit chemical weapons program.

Russia denied involvement in both incidents despite overwhelming evidence to the contrary.

There have been other cases of chemical weapons attacks in which Russia has been heavily suspected of involvement or at the very least, complicity in their use.

Incidents have included the poisoning in 2004 of Ukraine's then pro-Western President Viktor Yushchenko with dioxin, and the fatal poisoning of Alexander Litvinenko, a former KGB officer and critic of Putin who died in London after drinking green tea laced with polonium-210, a rare and potent radioactive isotope. A 2016 inquiry found Putin probably approved the killing. The Kremlin denied any involvement in either incident.

Then, when Russian troops fought alongside Bashar Assad's government forces in Syria's civil war in which the nerve agent sarin was used against civilians, killing over 1,400 people, Russia was accused of helping Syria to cover up the crime. Russia and Syria denied any use of chemical weapons but the OPCW's inspectors found undeclared toxins and munitions during site visits and in 2020, the chemical weapons watchdog condemned Syria's use of banned sarin and chlorine bombs.

When it comes to Ukraine now, we cannot say for sure whether Putin could or will use any kind of chemical weapons. But with Russia's reputation preceding it, close observers of Putin's regime suspect that he could have few qualms to deploy the same tactics again, and say the threat is a credible one.

"Are they capable of using low-grade chemical weapons in some form in Ukraine? They are, they did it in Syria. Yes, in a sense, it was through the regime, but I think they could [do it again]," Ian Lesser, vice president of think tank the German Marshall Fund of the United States, told CNBC.

Meanwhile, Wojciech Lorenz, a senior analyst at the International Security Programme at The Polish Institute of International Affairs, told CNBC that "you can never know" what Russia will do, but when it comes to the threat of chemical weapons use, "you have to treat it seriously."

"Russia has already used chemical weapons on the territory of NATO. They used chemical weapons in Britain, they used chemical weapons to poison and in their attempts to kill Navalny ... and it clearly indicates that they have chemical weapons that they should not have because they signed the chemical weapons treaty," he said.

Andrew Weber, former assistant secretary of defense for the Obama administration, and who now sits on the nonprofit Council on Strategic Risks, said this weekend that aside from the chemical weapons that have been associated with Russia in past incidents, some kind of biological weapon could be used instead.

"I think we need to take it very seriously, especially given the escalation of the disinformation campaign by Russia," he told New Zealand Radio's Morning Report on Saturday. As well as the possible use of chemical weapons, he said Russia could deploy biological weapons in Ukraine which the U.N. defines as disease-causing organisms or toxins disseminated with the intention to harm or kill humans, animals or plants. 

"Biological weapons would be different. They might use something like anthrax, for example, which is not contagious and wouldn't spread back to Russia. But the Russian illegal biological weapons program includes things like plague, tularemia [a rare infectious disease] and even smallpox," he said.

Both chemical and biological weapons are used to terrorize the opponent, and to cause mass casualties, he said. But he expected a massive response from the West should Russia resort to using them, saying "all bets would be off, there would definitely be a very very strong, united international response to any use of chemical or biological weapons."

Desperate measures

The danger in the Ukraine conflict, analysts point out, is that Putin might resort to ordering the use of chemical weapons if he feels that the armed forces are not making progress in seizing and occupying Ukraine, particularly as Ukraine's forces and volunteer fighters mount a staunch resistance and vow to fight to the death.

"I believe strongly that if the Russian forces get bogged down, and they will from time to time, that Putin will authorize the use of chemical weapons. He's done it before and he's likely to do it again since he is focused single-mindedly on taking over all of Ukraine and anything that deters or detracts from his ability to do that then he's going to react accordingly," retired U.S. Army Colonel Jack Jacobs told CNBC's Shepard Smith late Friday.

He noted that Russia's indiscriminate bombing of hospitals and other civilian targets has shown its increasingly uninhibited approach to the war in Ukraine as it seeks to make strides into Ukraine's territory.

"He's capable of doing anything as he is single-mindedly focused on one thing and that is taking over Ukraine," Jacobs said.