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
The 19-year-old, who appears in an ITV Tonight programme on gender identity, describes what it is like to live life as a trans man.
ITV's Tonight looks at the debate about transgender people - particularly among the young - and the pace of change around gender diversity.
Downing Street has hit back at Stormzy by stating Theresa May is "absolutely committed" to supporting people affected by the Grenfell fire.