The US and UK are investigating the extent of a terror threat after explosives were found in two packages bound for the US from Yemen.
The packages were found in the UK and Dubai on two overnight cargo planes in transit from Yemen on Friday.
President Barack Obama said the devices were a "credible terrorist threat".
UK Home Secretary Theresa May said experts were trying to establish whether the package found in Britain was "a viable explosive device".
Mr Obama's top counter-terrorism adviser John Brennan said: "The United States is not assuming that the attacks were disrupted and is remaining vigilant."
The discovery of the packages on FedEx and UPS cargo planes triggered security alerts in the US, UK and Middle East. Other planes at US airports were checked because they were thought to contain items from Yemen.
US officials later said that the two packages had been made inert.
The device found in Britain's East Midlands Airport was reportedly an ink toner cartridge that had been modified.
The packages were destined for Jewish places of worship in Chicago, Mr Obama said.
The alerts were:
- Suspect package found at Dubai
- Suspect package found at East Midlands Airport, UK
- Three cargo planes owned by the freight company UPS searched in Newark and Philadelphia
- US fighter jets escorted Emirates flight 201 from Dubai into New York, with officials saying the action was being taken "out of an abundance of caution" because cargo from Yemen was on board
- Suspect package from Yemen examined on a delivery lorry in New York
- BA flight from London to New York met by authorities amid reports of search of its cargo
Speaking at a White House press conference late on Friday, President Obama said that "an initial examination of those [two] packages has determined that they do apparently contain explosive material".
"Although we are still pursuing all the facts, we do know that the packages originated in Yemen.
"We also know that al-Qaeda in the Arabian Peninsula - a terrorist group based in Yemen - continues to plan attacks against our homeland, our citizens and our friends and allies."
He stressed that new aviation security measures were being taken in light of the alert by the Department of Homeland Security, "including additional screening".
John Brennan added: "It does appear there were explosive materials in both of the packages. They were in a form that was designed to try to carry out some type of an attack. The initial analysis is that the materials that were found and the device that was uncovered was intended to do harm."
The White House later said Saudi Arabia had provided information that helped identify the threat.
The UK's Daily Telegraph reported that an MI6 officer responsible for Yemen had received a tip-off.
FedEx and UPS suspended all their shipments out of Yemen, saying they would fully co-operate with investigators.
Speaking in London early on Saturday, Mrs May said that "at this stage I can say that the device [found in Britain] did contain explosive material".
"The forensic work continues," she said, adding that the British government's emergency committee, known as Cobra, had met on Friday and would hold another meeting later on Saturday.
"We are reviewing the security measures for air freight from Yemen and are in discussion with industry contacts," she said.
US officials told Associated Press they believed the packages contained PETN (pentaerythritol tetranitrate) - the same powerful explosive used in the failed bombing of a US-bound airliner last Christmas Day. However, the officials said that full testing had not been completed.
US security services remain on a high level of vigilance in the wake of the attempted Times Square bombing in May and the alleged attempted Christmas Day attack.
TAKEN FROM BBC : THIS IS A KUFFAR SOURCE SO WE MUST BE CAREFUL WITH WHAT THEY SAY AND DO NOT BELIEVE ANY CLAIMS THEY MAKE UNLESS VERIFIED BY THE MUJAHIDEEN.