The US has issued a global travel alert for its citizens in response to "increased terrorist threats".
The country's state department said "current information" suggested the Islamic State group, al-Qaeda, Boko Haram and others continued "to plan terrorist attacks in multiple regions".
The alert is to remain in place until 24 February 2016.
There have been deadly terrorist attacks in France, Russia, Mali and several other countries during the past month.
France, Belgium and other European nations are on high alert following the co-ordinated attacks in Paris, claimed by Islamic State (IS), which left 130 people dead.
Belgium has extends a maximum-security alert in Brussels for a week as a manhunt goes on for Islamic State suspects.
In the days following the attacks French President Francois Hollande said France was "at war" with Islamic State.
France has hit back at the group, bombing IS in Syria and Iraq. The US and its allies, as well as Russia, are also attacking IS to varying degrees.
Security is now extremely tight across France. Under the existing state of emergency, French police have greater powers to search premises and detain suspects.
A week after the Paris attacks, 20 people at the luxury Radisson Blu Hotel in Mali's capital Bamako were killed in a gun attack. Al-Qaeda in the Islamic Maghreb (AQIM) and its offshoot al-Murabitoun have said they were behind it but some doubt remains.
Mali state television showed images on Monday of two dead men that it said were the "authors" of the attack and appealed for information as to their identity.
The US alert advises its citizens to "exercise vigilance when in public places or using transportation".
They are also advised to "be aware of immediate surroundings and avoid large crowds or crowded places".