Russia has allegedly dropped the world's largest non-nuclear weapon on Isis. If reports are to be believed, it would be the first time the bomb has been used in combat.

Dubbed the "Father of all Bombs", or FOAB, reports say the weapon was dropped on the city of Deir ez-Zor, an Isis stronghold. There has so far been no confirmation on whether or not it was actually dropped on Isis, apart from a few tweets and online rumours.

The FOAB is formally known as the Aviation Thermobaric Bomb of Increased Power (ATBIP) and Russia is very secretive about it. In fact, there are almost no official pictures or video of the bomb itself, but there are videos of the actual test explosion and after-effects of the bomb, widely reported by Russian news outlets when it was first built in 2007.

FOAB has the yield of 44 tons of TNT and is smaller, but four times more powerful, than its American counterpart – the Massive Ordinance Air Blast or MOAB– which is also known as the "Mother of all Bombs" and has an equivalent TNT yield of 11 tons. That makes the FOAB the largest "droppable" bomb in military history. The US dropped the MOAB in April this year in Afghanistan.

FOAB is a thermobaric weapon – it causes damage by both explosive blast pressure as well as through the intense heat wave that follows. Thermobaric explosives are set off in the air above the target to inflict maximum damage and not used on the ground like traditional bombs.

In comparison to the MOAB, the FOAB is smaller and uses seven tons of explosive material, while the MOAB uses over eight tons. The epicentre of the blast for the FOAB is around 300 metres and the MOAB's is around 150 metres.

"The main destruction is inflicted by an ultrasonic shock wave and an incredibly high temperature. All that is alive merely evaporates," Aleksandr Rukshin, deputy chief of armed forces general staff, said at the time of the test back in 2007.

The videos released during initial test showed a four-storey building being obliterated. FOAB was described "as potent as an atomic explosion, but without the radioactive fallout".

The two bombs are also delivered in different ways. MOAB is carried over the target with a large aircraft bomber and released by opening the rear cargo door, while the FOAB is reportedly slowed down in its descent with the help of parachutes. Despite claims by Russia that the bomb is guided by their Glonass – proprietary Russian GPS – it is reported to be an unguided bomb.

The Russian defence ministry reportedly had said that the development of such bombs does not violate any international arms agreements.