The U.S. State Department is citing increased terrorist threats from militant groups around the world for its global travel alert to Americans. It's not advising people against travel but says U.S. citizens should be vigilant, especially in crowded places. The warning comes as millions of Americans prepare to travel for the U.S. Thanksgiving holiday on Thursday. The State Department website carries a statement saying current information suggests militant groups were continuing to plan attacks in multiple regions. It doesn't make any specific mention of the Paris attacks on November 13th claimed by Islamic State. It does, however, note that militants have carried out attacks in France, Nigeria, Denmark, Turkey and Mali during the past year.