In an extremely gruesome tactic, Islamic State militants in Iraq are stuffing hundreds of live scorpions inside bombs and launching them to incite fear among their enemies, according to a British military expert who returned from the country last week.

Poisonous varieties of scorpions packed inside 2-ft canisters are being blasted into towns and villages, which then explode on impact - scattering the scorpions and causing panic among civilian areas in the north of the country, senior Iraqi officials revealed.

"It's madness. ISIS has improvised devices to launch them," Hamish de Bretton-Gordon, ex-head of chemical and biological weapons for the Army and NATO, told The Mirror. "They promote the fact that they are doing it and it creates panic."

The latest terror weapon in Iraq is actually thousands of years old and was first used by Iraqis fighting against the Roman Empire.

"Scorpions are robust - even if they are launched a couple of miles, when the canister breaks thousands are flung out and start crawling all around," he said. "Some scorpions are very poisonous but the main thing is creating fear."

Although the bombs are not causing mass casualties, they are creating a profound "psychological impact," de Bretton-Gordon, who returned from Baghdad last week where he was advising security forces, said.

In "Greek Fire, Poison Arrows & Scorpion Bombs: Biological and Chemical Warfare in the Ancient World," author Adrienne Mayor describes how Iraqi soldiers would spit on the end of the scorpion to calm the creatures before they were packed into pots, which were then flung at the besieging Roman armies marching towards  the fortress city of Hatra, UK MailOnline reported.

"It was the brute effectiveness of Hatra's defensive biological and chemical weapons that overcame Roman morale, manpower and siege machines," Mayor, a historian of ancient science and classical folklorist, writes in her 2004 book. "The terror effect would be quite impressive."

Last week, the U.S. confirmed it had launched a further 20 airstrikes against ISIS targets, including raids near Sinjar, Qaim, Ramadi, Mosul and Samarra, as well as inside Kobane.

Earlier in the month, an ISIS-affiliated Twitter account revealed that a "dirty bomb" made out of 88 pounds of radioactive Uranium is allegedly in the possession of Islamic State militants.

The uranium, which had gone missing from Mosul University, has reportedly been weaponized and turned into what was described to be a "dirty bomb," a special improvised explosive device consisting of radioactive nuclear waste and conventional explosives, designed to spread hazardous radioactive material over a wide ranging area.

"A dirty bomb set off in an urban area would render at least several blocks off-limits while a lengthy cleanup process ensued," a report from Catholic Online stated. "Imagine if no traffic could pass through Times Square or across the busiest city thoroughfare near you."