The US has issued a worldwide travel alert for its citizens due to "increased terrorist threats".
"Current information suggests that ISIL, al Qaeda, Boko Haram and other terrorist groups continue to plan terrorist attacks in multiple regions," the State Department said.
"These attacks may employ a wide variety of tactics, using conventional and non-conventional weapons and targeting both official and private interests."
It cited recent attacks in Denmark, France, Mali, Nigeria and Turkey.
"US citizens should exercise vigilance when in public places or using transportation," the statement added.
Americans were also advised to avoid large crowds or crowded places and to "exercise particular caution during the holiday season".
The travel alert will be in place until 24 February.
It follows simultaneous attacks at several location in Paris that killed 130 people, and a hotel siege in which 19 people died in Mali.
Brussels spent much of the last few days in lockdown due to an "imminent" terrorist threat.
"Extremists have targeted large sporting events, theatres, open markets and aviation services," the alert added.
The State Department said "the likelihood of terror attacks will continue as members of ISIL/Daesh return from Syria and Iraq".
The US regularly issues individual country travel alerts, but worldwide alerts are rare.
Suspected suicide belt
Meanwhile hunting Paris terror suspect Salah Abdeslam have recovered a suspected suicide belt near where he is thought to have been on the night of the attacks.
The object found in a dustbin in the Paris suburb of Montrouge has "the same configuration" as suicide belts used by others involved in the attacks, according to a police source.
Abdeslam is suspected of playing at least a logistical role in the coordinated shooting and suicide bombings on 13 November and police say phone location data places him in Montrouge that evening.
It comes as the 26-year-old fugitive's brother Mohamed suggested Abdeslam may have decided not to go ahead with the attack at the last moment.
Another theory suggested by police is that Abdeslam, if he was involved in the attacks, may have had a technical problem with his belt.
Abdeslam's other brother, 31-year-old Brahim, died after his suicide belt exploded outside a café during the attacks, injuring 15 people.
The pair from Belgium had a heated argument the night before the massacres according to friends living in Brussels. One friend told television channel France 2 the disagreement appeared to be over money.
"I heard an argument, a massive argument," he said.
"I leaned against the window and I saw the two brothers. They were there. They were fighting each other."
In a statement released the day after the assaults, IS spoke of simultaneous attacks in the 10th, 11th and 18th arrondissements by eight "brothers wearing explosive belts".
Seven suicide bombers died: two at the Bataclan concert venue, three at the Stade de France, one at a cafe on Boulevard Voltaire and one during a police raid at an apartment in Saint-Denis.
There was no attack on the 18th district.
Francois Molins, the Paris anti-terror prosecutor in charge of the investigation said the vests used in the attacks were composed of acetone peroxide, a chemical explosive easy to produce by amateurs.
Police are continuing to focus their investigations on Brussels which remains on maximum alert.
Following raids at the weekend prosecutors charged a fourth person with terrorist offences linked to the attacks but released 15 others.
Alex Thomson, chief correspondent with Channel 4 News, is in Brussels. He told Newstalk Breakfast the situation there is improving.
