On Monday, human rights organizations and Ukraine’s envoy to the United States accused Russia of using cluster and vacuum bombs against Ukrainians, weapons that have been denounced by a number of international organizations.

Russian soldiers appeared to have used widely banned cluster munitions, according to Amnesty International and Human Rights Watch, with Amnesty accusing them of targeting a preschool in northern Ukraine while civilians took shelter inside.

After meeting with members of the US Congress, Ukraine’s ambassador to the US, Oksana Markarova, informed reporters that Russia employed a thermobaric weapon known as a vacuum bomb in its invasion of her nation.

After a meeting with MPs, Markarova said, “They used the vacuum bomb today.” “…The destruction that Russia is attempting to wreak on Ukraine is massive.”

A vacuum bomb, also known as a thermobaric weapon, draws oxygen from the surrounding air to produce a high-temperature explosion with a blast wave that lasts much longer than a normal explosive and is capable of vaporizing human beings.

The employment of thermobaric weapons in the Ukrainian conflict has not been officially confirmed. Early Saturday afternoon, CNN reported that one of its teams had observed a Russian thermobaric multiple rocket launcher near the Ukrainian border.

Jen Psaki, the White House press secretary, said she had read stories but couldn’t confirm whether Russia had used such weapons. “If that is accurate, it might be a war crime,” she said at a press conference, adding that international organizations would review the situation and that President Joe Biden’s government “would try to be a part of that dialogue.”

Requests for comment to the Russian embassy in Washington went unanswered.

Ukraine, according to Markarova, is actively working with the Biden administration and Congress to secure more weaponry and stiffer sanctions.

She told reporters following the meeting, “They should pay, and they should pay a hefty price.”

Democratic Representative Brad Sherman, who attended the conference, said the Ukrainians had requested a US-enforced no-fly zone above Ukraine, but he thought that was too risky since it could lead to conflict with Russia.

International humanitarian law, according to Amnesty International, prohibits the use of weapons that are inherently indiscriminate, such as cluster munitions. It is a war crime to launch indiscriminate assaults that kill or hurt civilians.