Federal officials are urging vigilance ahead of the one-year anniversary of the death of Osama bin Laden, NBC News has learned.
The advisory released late Wednesday does not cite a specific or credible threat, but says authorities are concerned that "lone wolf" terrorists might try to use the May 1 anniversary to avenge the death of the al-Qaida leader.
Officials stressed that the advisory was released out of "an abundance of caution" as the one-year anniversary of bin Laden's death approaches.
NYPD spokesman Paul Browne said Thursday that the city remained ever-alert.
"There's no known specific threat to the city because of the anniversary," he said, "but the NYPD continues to maintain a robust counterterrorism posture regardless of anniversaries because of past and repeated interest demonstrated by terrorists in returning here to kill New Yorkers."
Bin Laden was shot and killed by a team of Navy SEALS who stole into his Afghanistan compound in a daring overnight raid. Officials said his body was buried at sea.
Once the world's most wanted terrorist, bin Laden claimed full responsibility for the 9/11 attacks several years after the towers fell.
Khalid Sheikh Mohammed, the self-professed mastermind of the attacks and an alleged bin Laden deputy, is awaiting military trial in Guantanamo Bay with four co-defendants, charged with the murder of nearly 3,000 people, terrorism, hijacking an aircraft, conspiracy and attacking civilians.
They are scheduled to be arraigned next month.
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