WASHINGTON - A bomb expert who is said to have created the "underwear bomb" used in the 2009 failed terror attack on a Detroit flight has joined the group of Islamic militants advancing into Iraq.

Ibrahim Hassan al-Asiri, Al-Qaeda's chief bomb-maker, has recently pledged allegiance to the Islamic State of Iraq and Syria or ISIS, according to intelligence reports reaching the U.S. capital.

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The successful advance of ISIS militants into a wide swath of Iraqi territory has reportedly inspired top terrorists like al-Asiri to become eager recruits of the ISIS.

Intelligence officials who requested anonymity say Hassan al-Asiri is the guy that keeps them awake at night because they never know what he is up to next.

In the summer of 2009, he was responsible for building a bomb from a powdery explosive that was hard to detect, which he inserted into the rectum of his brother, Abdullah al-Asiri.

The younger al-Asiri was on a mission to kill Saudi Arabia's Prince Mohammed bin Nayef, who survived the attack with a slight head injury while al-Asiri died.

Then in December of that year, on Christmas day, Hassan al-Asiri put together an "underwear bomb" that was used in an attempt to blow up a Northwest Airlines flight bound for Detroit with 289 people on board.

The new type of bomb was smuggled into the plane by Nigerian Umar Farouk Abdulmutallab, then 23, by hiding it in his underwear.

The bomb failed to detonate as the flight descended on Detroit but caused a fire that engulfed Abdulmutallab, who later told the court that he participated in the terror plot to avenge the killing of Muslims by the U.S.

Abdulmutallab is serving a life sentence that was handed down by a U.S. court in February 2012.

Despite the failure of his two explosive devices, Hassan al-Asiri developed yet another 'ingenious' bomb in 2010: printer cartridge stuffed with 400 grams of PETN, which is similar to ink toner powder, and connected it to a timer and detonator inside a laser printer.

The printer bombs were then brought to UPS and FedEx branches in Yemen, where they were loaded into cargo planes bound for the U.S, but were intercepted by Dubai and British authorities.

With Hassan al-Asiri joining the ISIS, the intelligence community believes that it may not take long before the group would mount a deadly terror attack directed to the U.S. and its allies.

Already, the U.S. government on Thursday alerted its citizens after it received classified information on an 'imminent threat' on the main airport of Uganda.

Following the U.S. announcement, the United Kingdom also stepped up its airport security on US-bound flights, subjecting travelers from Europe and the Middle East to more rigid screening over fears that Islamic jihadists may slip bombs into planes undetected.

TagsIbrahim Hassan al-Asiri, ISIS, ISIL, Al-qaeda