The concerns, according to six people with knowledge of the matter, come amid a push by the administration to ensure allies are prepared for such an event, as well as to mobilize new resources and investments in manufacturing of detection systems for when the chemicals are used.But in the case of continued battlefield losses, or a complete collapse of the Russian army, some top officials working on the issue have determined that Moscow might resort to employing chemical weapons — including those the country has been associated with using in the poisoning of Alexei Navalny.Some chemicals could be used for a mass casualty attack even though Moscow has been known to use the nerve agent Novichok against one or two people at a time, officials and experts said.The U.S. ramped up efforts to track Russia’s use of Novichok, a nerve agent, after the international community linked it to the poisoning of Navalny, an outspoken opponent of Putin, and Sergei Skripal, a British citizen who used to work as a Russian intelligence officer.And in 2020, Navalny was hospitalized in Germany where officials said there was “unequivocal proof” he was poisoned via Novichok while aboard a flight."