A transatlantic terror alert was sparked last night after explosive material was discovered on a plane at a UK airport and on another aircraft in Dubai.
One device was discovered on a plane which had stopped to refuel at East Midlands Airport in the UK while flying from Yemen to Chicago.
It was apparently made from a converted ink toner cartridge, which contained white powder and had wires sticking out from the top.
The second was found on a plane in Dubai, which had also flown from Yemen and was on its way to the US.
The discovery prompted cargo planes to be searched at two US airports and a package found on a delivery vehicle in New York was also checked after reports a suspicious package was on board.
US President Barack Obama warned that the terror threat posed by the packages was “credible” amid a major security alert in US cities.
The President said the packages, which originated in Yemen, had both contained explosive material and the targets appeared to be two synagogues in Chicago.
Mr Obama said he would be seeking greater “co-operation” with the state in order to tackle the activities of an al Qaida offshoot, and urged the public to be “vigilant”.
Speaking in the White House, Mr Obama said: “I want to briefly update the American people on a credible terrorist threat against our country and the action that we have taken with our partners to respond to it.
“Our intelligence and law enforcement professionals working with our friends and allies identified two suspicious packages bound for the US — specifically, two places of Jewish worship in Chicago.
“Those packages have been located in Dubai and East Midlands Airport in the UK.
“Initial examination of those packages has determined that they do apparently contain explosive material.”
The president's comment seemingly contradicts earlier suggestions that the package found in Britain did not contain any explosives.
Mr Obama said he had instructed officials to take “whatever measures were necessary” to protect Americans, and planes in Newark and Philadelphia had been searched as part of tougher cargo screening.
“We will continue to pursue additional protective measures for as long as it takes to ensure the safety and security of our citizens,” he added.
“I have also directed that we spare no effort in investigating the origins of these suspicious packages and their connection to any additional terrorist plotting.”
A spokesman for the Metropolitan Police's counter terrorism command, which took responsibility for the operation from Leicestershire Police, said: “A number of items have been sent for additional scientific examination. At this stage there is nothing to suggest any location was being targeted in the UK.”
In the US, two UPS planes in Philadelphia and a third jet in Newark, New Jersey, were moved away from terminal buildings to be examined.
In Brooklyn, New York, police were examining a package from a UPS truck after reports that a possible explosive had been found. The planes in Philidelphia had arrived from Cologne and Paris while the plane in Newark had arrived from East Midlands Airport.
Cargo subject to same checks as travellers
Freight carried by air has to go through the kind of stringent checks that airline passengers on commercial flights are all too aware of.
Security measures in the UK are regulated by the Aviation and Maritime Security Act 1990.
This means that all air freight consignments must either be screened or originate from a Department for Transport (DfT) accredited known consignor before being loaded on to an aircraft.
Listed cargo agents or in-flight supplies companies are among those invited to attend a threat assessment training course organised by the DfT's transport security body Transec.
Those attending will be able to organise and conduct initial and recurrent training courses in recognition of firearms, explosives and incendiary devices for transport security personnel.
“Cargo undergoes exactly the same kind of security checks as airline passengers do,” said David Learmount, operations and safety editor of Flight Global.
“Before any package goes on to a plane it gets screened. In commercial flights as soon as passengers buy tickets they are being checked. It's the same with air freight.”
Mr Learmount said freight had always been a potential target for terrorists but bombers had concentrated on passenger aircraft.
An air security expert said the heightened state of alert worldwide has made people more vigilant about potential threats.
Norman Shanks, former head of group security of BAA, said:
“It wouldn't be surprising if there were false alarms after the package was found this morning. It's just part of the pattern. People are much more keyed up to it and are reacting on the basis of being safe rather than sorry.”
The Transportation Security Administration in the US has in place what it describes as a “multi-layered, high-tech, industry-cooperative” approach to screening cargo. It also carries out “robust” background checks on cargo |employees.
However, the US Department of Homeland Security has already said it is to enhance security, with measures including heightened cargo screening, in light of today's developments.