“They used the vacuum bomb today, which is actually prohibited by the Geneva convention,” Ambassador Oksana Markarova said after a meeting with lawmakers. “The devastation that Russia is trying to inflict on Ukraine is large.”

She said Ukraine was working actively with US President Joe Biden’s administration and Congress to obtain more weapons and tougher sanctions.

“They should pay, they should pay a heavy price,” she told reporters after leaving the meeting.

One lawmaker who attended the meeting, Democratic Representative Brad Sherman, said the Ukrainians had asked for a US-enforced no-fly zone over Ukraine but that he felt that was too dangerous because it could provoke conflict with Russia.

A vacuum bomb uses oxygen from the surrounding air to generate a high-temperature explosion, typically producing a blast wave of a significantly longer duration than that of a conventional explosive.