US security officials say they are investigating a credible terror threat to the nation ahead of the 10th anniversary of the 9/11 attacks.
“In this instance, it’s accurate that there is specific, credible but unconfirmed threat information,” the Department of Homeland Security said.
“We have taken, and will continue to take all steps necessary to mitigate any threats that arise,” it added in a statement.
The department noted that in the US raid that killed al-Qa’ida leader Osama bin Laden in May, documents and computer files seized at this compound showed the terror network had pondered strikes to coincide with Sunday’s anniversary, including against American trains.
“We continue to ask the American people to remain vigilant as we head into the weekend,” it said.
The announcement came after the Pentagon on Wednesday raised the alert level at bases across the United States as “a prudent and precautionary measure,” given al-Qa’ida’s interest in milestones and anniversaries.
US media reported that the threat possibly targeted Washington or New York but homeland security officials did not confirm those accounts.
NBC said talks were underway on whether to raise the US alert status before the anniversary of the attacks, when nearly 3,000 people were killed in an al-Qa’ida plot against the United States.
US Navy commandos tracked down and killed bin Laden at his hideout in the Pakistani garrison town of Abbottabad in May.
The biggest event will be the reading of victims’ names at Ground Zero, which will be attended by victims’ family members, President Barack Obama, former president George W Bush, and New York Mayor Michael Bloomberg.
Although there have been no attacks on the scale of 9/11 in the United States in the 10 years since, the nation has been on heightened alert amid a series of foiled and failed attacks.
Security is the main concern among organisers of the ceremonies remembering those who died and large crowds are expected as the country reflects on a decade of war abroad and fear of further attacks at home.
A decade on, America is marking 9/11 with a series of events to honour those who died when hijackers crashed planes into the World Trade Center, the Pentagon, and a field in rural Pennsylvania.