India, May 22 -- The cost of the US-led military campaign against Iran is mounting sharply, with new estimates suggesting that Tehran has destroyed nearly $1 billion worth of America's prized MQ-9 Reaper drones since the conflict began in February.

At least 24 MQ-9 Reapers, and possibly as many as 30, have been lost during the war, according to a person familiar with the matter cited by Bloomberg. The figure includes drones that were damaged during operations and later written off. The losses amount to nearly 20 per cent of the Pentagon's prewar inventory of the high-value unmanned aircraft.

Many of the drones were reportedly shot down mid-flight by Iranian fire, while others were destroyed on the ground in missile strikes or lost in ac...