The MoD said its Russian counterpart had confirmed the use of thermobaric rockets creating “incendiary and blast effects” in the invasion.
A video posted to Twitter by the MoD said the weapons were used by Russia in both Afghanistan and Chechnya.
Thermobaric weapons are not illegal but their use is strictly regulated, MoD said.
It comes as the MoD said the Russian state “almost certainly maintains extensive links” with Russian private military companies (PMCs) and is “likely deploying” their mercenaries to Ukraine.
“Russian PMCs have been accused of committing human rights abuses in several countries, such as Syria, Libya and the Central African Republic, whilst operating on behalf of the Russian state,” the MoD said.
What is a vacuum bomb?
Vacuum bombs, also known as thermobaric weapons, withdraw oxygen from the air around them to create an explosion with a longer blast wave at a much higher temperature which means they have the potential to vaporise human bodies.
Rather than using a mix of fuel and oxygen within the bomb itself, thermobaric weapons consist largely of fuel resulting in potential to cause great destruction when launched.
The weapons were first developed by the United States for use in the Vietnam War and have since been used in multiple conflicts including the Soviet-Afghan War in the 1980s as well as by US and UK forces during the War in Afghanistan.
Are vacuum bombs banned?
Thermobaric weapons such as vacuum bombs are banned internationally as per the terms of the Geneva Convention, 110 signatories agreed to the Cluster Munitions Convention, however the US, Ukraine and Russia are some of the 74 states who did not agree to the convention.
British Defence Secretary Ben Wallace said the UK has been supplying Ukrainian forces with weapons, including 3,615 anti-tank weapons, known as NLAws, or new light anti-tank weapons.
What has been said about chemical weapons?
The United States has warned that Russia may seek to use chemical and biological weapons in Ukraine.
Russian ministry of foreign affairs spokesperson Maria Zakharova made unfounded accusations that Ukraine was developing such weapons with the help of the United States.
White House press secretary Jen Psaki said the world should be “on the lookout” for the Russian use of chemical and biological weaponry.
She said: “We took note of Russia’s false claims about alleged US biological weapons labs and chemical weapons development in Ukraine. We’ve also seen Chinese officials echo these conspiracy theories.
“This is all an obvious ploy by Russia to try to justify its further premeditated, unprovoked, and unjustified attack on Ukraine.
“Now that Russia has made these false claims, and China has seemingly endorsed this propaganda, we should all be on the lookout for Russia to possibly use chemical or biological weapons in Ukraine, or to create a false flag operation using them. It’s a clear pattern.”