Russian TV showed a Tupolev bomber dropping the bomb over a test range, a powerful explosion and a four-storey building reduced to rubble.
Claims it is bigger than the Moab, a US device of similar destructive power, seem plausible, analysts say. Such bombs are mainly designed to destroy underground targets.
Fuel-air bombs, technically known as thermobaric devices, generally detonate in two stages: a small blast creates a cloud of explosive material, which is then ignited with devastating effect