Officials believe two mail bombs intercepted Friday were assembled by Al Qaeda's top bombmaker.
Investigators believe Ibrahim Hassan al-Asiri designed the bombs authorities found in Dubai and the United Kingdom.
The 28-year-old Saudi national is also believed to have designed the so-called underwear bomb that Umar Farouk Abdulmutallab attempted to ignite aboard a Detroit-bound airliner on Christmas Day.
The two bombs discovered in England and Dubai likely would have made it onto flights bound for the U.S. if not for a tip from the Saudi government. The shared intelligence could signal a new era of cooperation in the war against Al Qaeda.
Counterterrorism officials are now warning local law enforcement and emergency personnel to look out for mail that could have dangerous substances hidden inside, as investigators scan for more mail bombs possibly sent from Yemen.
The FBI and Homeland Security Department say packages from a foreign country with no return addresses and excessive postage need to be scrutinized.
The information came from an advisory sent to local officials around the country obtained by The Associated Press.
Mail bombs were sent in packages addressed to Jewish synagogues last week.
Authorities have said the explosive devices bore the hallmarks of /*Al Qaeda*/ and the terrorist group's Yemen offshoot is suspected of mailing the bombs. After a frenzied day of searches in Philadelphia, Newark, N.J., and New York City, no explosives were found inside the United States.
An official security source said Monday that United Arab Emirates authorities are tracing the serial numbers of a mobile phone circuit board and computer printer used in the mail bombs.
Meantime, a team of U.S. investigators is on its way to Yemen to help search for suspects in that mail bomb plot.
U.S. officials say they still don't know if they've found all of the bombs that were part of the plan.
The government thinks the two seized printer bombs may have been designed to blow up planes in flight.
Investigators also believe they may have been designed by the bomb maker behind the failed underwear bombing last Christmas.
Authorities say Al Qaeda may be more focused now on attacking the U.S. than at any time since 911.
"I think they want to inflict damage, death and destruction on the United States, and we're going to have to now look for a whole wide range of tactics," said former secretary of Homeland Security Michael Chertoff.
ABC news has learned that the government is reviewing all shipments from Yemen from the past two weeks to determine if any packages are already here.
Authorities released the woman they thought originally sent the packages saying she may have been a victim of identity theft.
The /*Transportation Security Administration*/ is implementing the next phase of its secure flight screening program.
This comes as the /*TSA*/ begins more thorough pat downs of passengers at airports.
Beginning Monday, travelers must provide their full names as they appear on a current government issued photo ID, their date of birth and their gender.
If the airline cannot get TSA clearance of a name before a flight, that passenger will not fly.
The Associated Press contributed to this report.
