Packages found at a British airport and in Dubai contained explosives and represented a "credible terrorist threat", US president Barack Obama has said.
The president said the US-bound packages, which originated in Yemen and were found aboard cargo jets, appeared to be targeted at two synagogues in Chicago.
The president's comment contradicts earlier suggestions that the package found in Britain did not contain explosives.
A transatlantic terror alert was sparked after the discovery of one of the packages at East Midlands Airport on Friday morning. Police were called to a freight distribution centre at the airport after officials raised concerns during a routine search.
Workers found a toner cartridge which had been manipulated with wires attached to it, and a white powder, according to sources in the US.
The cargo was removed from an American-registered plane that arrived from Yemen and was en route to Chicago via Philadelphia, the Metropolitan Police said.
The cargo plane had landed at East Midlands Airport as part of a routine stop-over.
A number of items were sent for additional scientific examination, a Met spokesman said.
An official UAE security source said the Dubai device meanwhile was found in a courier company's regional hub.
The source said an investigation was under way, and added there had been "close cooperation between several intelligence and security agencies around the world following the discovery of shipments containing an explosive device originating in Yemen".
