US officials believe that the Nusra Front, al-Qaeda's affiliate in Syria, has been working with its Yemen affiliate, AQAP, to carry out operational testing of new bomb designs in Syria.
The new explosives the bombmakers are trying to design include non-metallic bombs, ABC News reported.
There are also concerns that US and Europe-bound planes could be targeted by foreign fighters with Western passports who spent time fighting for Islamist groups attempting to overthrow the regime of Syria's president Assad.
More top news
Daniel Rodriguez, also known as Grymey D, used Instagram, Facebook and Blackberry Messenger to contact girls who he invited to his home.
A grandmother burst into tears after her grandson played her surprise birthday messages recorded by her family.
Judge condemns pair who attempted to smuggle in migrants for their "greed" and "recklessness".