WASHINGTON (AFP) - 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 said.