Russia has been accused of attacking Ukrainians with cluster bombs and vacuum bombs, weapons that have been condemned by a variety of international organisations.
Amnesty International and Human Rights Watch both said that Russian forces appeared to have used widely banned cluster munitions, with Amnesty accusing them of attacking a preschool in north-eastern Ukraine while civilians took shelter inside.
Oksana Markarova, Ukraine’s ambassador to the United States, told reporters after meeting with members of the US Congress that Russia had used a thermobaric weapon, known as a vacuum bomb, in its invasion of her country.
“They used the vacuum bomb today,” Ms Markarova said.
“The devastation that Russia is trying to inflict on Ukraine is large.”
A vacuum bomb uses oxygen from the surrounding air to generate a high-temperature explosion, producing a lethal shock wave and sucking the oxygen from the lungs of anyone in the vicinity.
The bombs, also known as thermobaric warheads, typically produce a blast wave of a significantly longer duration than that of a conventional explosive and are capable of vaporising human bodies.
There has been no official confirmation that thermobaric weapons have been used in the conflict in Ukraine.
Ms Markarova said Ukraine was working actively with the US to obtain more weapons and tougher sanctions.
“They [Russia] should pay, they should pay a heavy price,” she said.
Democratic Representative Brad Sherman, who was in the meeting, said the Ukrainians had asked for a US-enforced no-fly zone over Ukraine, but he felt that was too dangerous because it could provoke conflict with Russia.