(NEXSTAR) —  The Ukrainian ambassador to the United States has accused the Russian military of deploying a “vacuum bomb” in Ukraine, and in a manner that would constitute a war crime.

“They used the vacuum bomb today, which is actually prohibited by Geneva Conventions,” said Oksana Markarova on Monday. “So, you know, the devastation that Russia is trying to inflict on Ukraine is large, but Ukrainians will resist.”

Thermobaric weapons, also known as vacuum bombs, aerosol bombs or fuel-air explosives (FAEs), are explosive devices that use atmospheric oxygen to create high-temperature explosions with larger blast waves, typically by dispersing a vapor cloud of fuel into the air prior to ignition. The resulting blast also creates a “pressure wave” and “subsequent rarefaction [vacuum], which ruptures the lungs,” the U.S. Defense Intelligence Agency said in a 1993 study, per a 2000 report on Russia’s use of vacuum bombs by Human Rights Watch (HRW).

“If the fuel deflagrates but does not detonate, victims will be severely burned and will probably also inhale the burning fuel,” the Defense Intelligence Agency added in its 1993 study, which stated that undetonated fuels are usually highly toxic and “should prove as lethal … as most chemical agents” if inhaled.

Officials have yet to independently confirm the use of vacuum bombs by the Russian military in Ukraine, though the White House has acknowledged such claims. A team with CNN had also reported seeing Russian military vehicles mounted with thermobaric launchers near the Ukrainian border.

On Monday, White House Press Secretary Jen Psaki said during a press briefing that the use of cluster munitions and “vacuum bombs” against Ukrainian civilians would potentially constitute war crimes.

“I don’t have any confirmation of that,” Psaki told a reported who asked about cluster munitions and vacuum bombs. “We have seen the reports. If that were true, it would potentially be a war crime.” Psaki added that “a range of international fora” would assess the criminality of such weapons usage.

Under the rules set forth by the Geneva Conventions, the use of thermobaric weapons could be a violation of Protocol III, which stipulates that incendiary weapons are prohibited in any locations where a “concentration of civilians” — such as “in inhabited parts of cities, or inhabited towns or villages” — may be present.

Ukrainian President Volodymyr Zelensky, meanwhile, has already called for Russia to be investigated for war crimes after an attack in part of Kharkiv where there were “no military targets.”

“Nobody will forgive. Nobody will forget. … This is state terrorism of the Russian Federation,” The Associated Press reported.

In addition to its alleged use of vacuum bombs, Amnesty International and HRW have accused Russia of using cluster munitions — devices that disperse smaller bombs — in Ukraine, at the site of a school where civilians were taking cover and a hospital. The controversial munitions are currently banned by an international treaty, though Russia and Ukraine are not among its signatories.