The Ministry of Defence says Russia has confirmed the use of thermobaric rockets – often called vacuum bombs – in Ukraine and is also “likely” deploying private mercenaries.

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.

Thermobaric munitions differ from other types in that they do not consist of a fuel and oxidising agent to ignite. Instead, the fuel is dispersed as a cloud and uses the atmospheric oxygen in ignition. As a result, they are much more powerful.

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.

The United States has warned that Russia may seek to use chemical and biological weapons in Ukraine.

It comes after 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.”

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.

He said a “small consignment” of Javelin anti-tank missiles is to follow, and ministers are considering whether to also send Starstreak high-velocity anti-air missiles.