.A credible but unconfirmed terrorism threat against New York City and Washington may be linked to al-Qaeda leader Ayman al-Zawahri, a US official said today.
Zawahri took the reins of al-Qaeda after Osama bin Laden was killed in May in a US raid in Pakistan.
President Barack Obama has ordered a redoubling of US counter-terrorism efforts in the face of the threat ahead of the 10th anniversary of the September 11, 2001 attacks
Washington DC and New York were targeted in al-Qaeda attacks a decade ago this Sunday that killed nearly 3,000 people.
In New York, police cars took up positions on midtown blocks on Lexington, Park and Fifth avenues today as officers stopped trucks and other vehicles for inspection. Drivers were made to open the storage spaces of delivery trucks for police.
In Brooklyn, US marshals armed with machine guns guarded the federal courthouse and increased security was seen in front of the nearby city emergency management office.
A police source said a manhunt was under way for two or three suspects. A US intelligence alert said operatives in the suspected plot may be carrying American documents.
But officials used strong caveats when discussing the threat information privately, with a national security official cautioning that experts thought the threat would ultimately not check out.
New York City Mayor Michael Bloomberg also stressed the threat had not been corroborated, even as he announced heightened security measures "some of which you may notice, some of which you may not notice".
"There is no reason for any of the rest of us to change anything in our daily routines," he told a news conference.
However, Mr Bloomberg asked citizens to report suspicious or dangerous activity, adding: "Over the next three days we should all keep our eyes wide open."
The White House said Mr Obama was briefed on specific threat information yesterday and noted that the US government had already "enhanced its security posture" ahead of the anniversary.
White House spokesman Jay Carney said: "We're hyper-vigilant to this specific report that's just coming in." He told MSNBC television that the US government was taking all necessary precautions, without offering details.
Documents discovered in Osama bin Laden's compound in Abbottabad, Pakistan, after he was killed in a raid in May by Navy Seals highlighted his persistent interest in attacking the United States around the anniversary of the 2001 attacks. But it is unclear if the plans ever evolved beyond aspiration.
Reuters