Al-Qaeda wants revenge for the death of terror leader Osama bin Laden and, on the one-year anniversary of the raid that led to his death, U.S. security officials are on high alert.
ABC News has learned that authorities are studying the possibility of terrorists using body bombs on U.S. flights coming in from overseas.
"The surgeon would open the abdominal cavity and literally implant the explosive device in and amongst the internal organs," Dr. Mark Melrose of Urgent Care Manhattan said.
At airports across the United States, security was stepped up in advance of Wednesday's anniversary of the death of bin Laden. A noticeable increase in police presence was observed at Metro stations throughout the D.C. area as well.
In D.C., New York and around any possible targets, a cloud of concern exists. And though some try to downplay its significance, the White House did the opposite: On Tuesday, President Obama arrived for a surprise visit to Afghanistan though he'd earlier said there'd be no excessive celebration.
Meanwhile, at the Pentagon Tuesday, they marked another anniversary - Ten years since the Pentagon Force Protection Agency was created, its special law enforcement division in the wake of 9/11 designed to protect the building and it's 23,000 employees from another attack.
"We have to be alert," New York City Police Commissioner Ray Kelly said. "We have not seen al Qaeda driven by dates.
U.S. and European authorities have warned that Al-Qaeda affiliates in Yemen have been designing the body bombs with no metal parts to get past airport security.
As a result of the potential threat, security has been stepped up at airports in the U.S., the United Kingdom and the Middle East.
A year ago, President Obama ordered the raid inside Pakistan to kill Osama bin Laden. On Monday, the president called on Americans to remember those who participated in the operation.
"The American people rightly remember what we as a country accomplished in bringing to justice somebody who killed over 3,000 of our citizens," he said.
U.S. authorities say they've made adjustments to airport screenings such as turning up the radiation used to make it easier to spot body bombs.