The United States issued a worldwide travel alert on Monday warning its citizens to increase vigilance in the wake of the deadly, coordinated attacks in Paris.

"Current information suggests that (Islamic State), al-Qaeda, Boko Haram, and other terrorist groups continue to plan terrorist attacks in multiple regions," the State Department said in a warning posted on its website.

Citing recent attacks in Denmark, France, Mali, Nigeria and Turkey, it also noted the threat of "lone wolf" attacks on public gatherings.

"Extremists have targeted large sporting events, theaters, open markets and aviation services," the alert said.

The warning follows the unprecedented deadly attacks in Paris and the subsequent manhunt for suspects that has put the Belgian capital Brussels in a virtual lockdown. The US State Department says further attacks remain a dangerous possibility.

"US citizens should exercise vigilance when in public places or using transportation," it said, advising Americans to avoid large crowds or crowded places and to "exercise particular caution during the holiday season."

Normal Thanksgiving holiday

But domestically, Washington's top domestic security figure said citizens should not be afraid to travel for the upcoming US Thanksgiving holiday.

"We have no specific credible intelligence about a threat of the Paris type directed at the homeland here," Homeland Security chief Jeh Johnson said Sunday, speaking on NBC's Meet the Press. "With this holiday season coming up we want the public to continue to go to public events, celebrate the holiday season, travel, be with their families and the like."

Police in European countries have been on heightened alert following the Paris attacks in which gunmen and suicide bombers struck without warning November 13, killing 130 people in near simultaneous attacks at several points across the city.

jar/jm (Reuters, AFP, AP)