Airports across the United States were put on high alert on Saturday after suspicious packages originating from Yemen were found, on a plane in UK, even as FBI is investigating whether it is a part of a terror group's rehearsal for a mail bomb attack.

"As a result of security precautions triggered by this threat, the additional measures were taken regarding the flights at Newark Liberty and Philadelphia International Airports," the White House press secretary, Robert Gibbs, said in a statement.

FBI and its counterparts in other countries are investigating whether these multiple suspicious packages found aboard UPS flights landing in Newark, NJ, Philadelphia and England are part of a terror group's rehearsal for a mail bomb attack.

US President Barack Obama was notified about it on Thursday night at 10.35 by John Brennan, assistant for homeland security and counter-terrorism.

Obama directed US intelligence and law enforcement agencies, and the Department of Homeland Security, to take steps to ensure the safety and security of the American people, and to determine whether these threats are a part of any additional terrorist plotting, the White House said.

The White House said on Friday night, intelligence and law enforcement agencies discovered potential suspicious packages on two planes in transit to the United States.

"Based on close cooperation among US government agencies and with our foreign allies and partners, authorities were able to identify and examine two suspicious packages, one in East Midlands, United Kingdom and one in Dubai. Both of these packages originated from Yemen," it said.

The Department of Homeland Security said as a precaution, it has taken a number of steps to enhance security. Some of these security measures will be visible while others will not. "The public may recognise specific enhancements, including heightened cargo screening and additional security at airports.

Passengers should continue to expect an unpredictable mix of security layers that include explosives trace detection, advanced imaging technology, canine teams and pat downs, among others.

As always, we remind the public to remain vigilant and report suspicious activity to local law enforcement," the statement said.

US officials believe that Al Qaeda in the Arabian Peninsula, commonly referred to as AQAP, is behind the plot, the CNN said. One suspicious package, found in Britain, contained a "manipulated" toner cartridge but tested negative for explosive material, sources were quoted as saying by the CNN.

It led to heightened inspection of arriving cargo flights in Newark, New Jersey, and Philadelphia, Pennsylvania, and a UPS truck in New York. The package had white powder on it as well as wires and a circuit board, a law-enforcement source said; someone shipped it from Sanaa, Yemen, with a final destination of Chicago, Illinois.
A similar package has been discovered in Dubai, in the United Arab Emirates, the source said. Investigators were looking for a "possible nexus to terrorism," a US official told CNN.

Meanwhile the FBI reported that two of the suspicious packages were addressed to religious institutions in Chicago. "All churches, synagogues and mosques in the Chicago area should be vigilant for any unsolicited or unexpected packages, especially those originating from overseas locations," Chicago FBI spokesman Ross Rice said.