US State Department issues worldwide travel alert ahead of tenth anniversary of 9/11 attacks

The US State Department on Friday issued a worldwide travel alert ahead of the 10th anniversary of the 9/11 attacks, calling on Americans living and traveling abroad to remain vigilant.

The department said it had not identified any "specific threats" about possible attacks but that Al-Qaeda and its affiliates had "demonstrated the intent and capability to carry out attacks" against the US and US interests.

"In the past, terrorist organizations have on occasion planned their attacks to coincide with significant dates on the calendar," the State Department said. The alert expires on January 2, 2012, it added.

Homeland Security Secretary Janet Napolitano said there was "no specific or credible intelligence that Al-Qaeda or its affiliates are plotting attacks" linked to the anniversary of the worst terror strikes on US soil. "We remain at a heightened state of vigilance, and security measures are in place to detect and prevent plots against the United States should they emerge."

US security is expected to be tight on September 11, when US President Barack Obama attends ceremonies at the three sites where the terrorists struck: the 'ground zero' site in Manhattan where the World Trade Center stood; the Pentagon outside Washington; and Shanksville, Pennsylvania, where a hijacked United Airlines jet crashed after passengers and crew fought back.