Citing "increased terrorist threats" from militant groups in various regions of the world, the U.S. State Department issued a global travel alert on Monday following deadly militant attacks in France and Mali.
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As millions of Americans prepare to travel for the U.S. Thanksgiving holiday on Thursday, the agency said potential attackers could target private or government interests.
"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.
Although it did not mention the November 13 Paris attacks claimed by the Islamic State group in which 130 died, the department noted that militants had carried out attacks in France, Nigeria, Denmark, Turkey, and Mali during the past year.
"Authorities believe the likelihood of terror attacks will continue as members of (Islamic State) return from Syria and Iraq," it said. "Additionally, there is a continuing threat from unaffiliated persons planning attacks inspired by major terrorist organizations but conducted on an individual basis.
Belgium charges fourth suspect
Belgian authorities have charged a fourth suspect with terrorism offenses after they detained 16 people on Sunday.
The federal prosecutor said in a statement that the suspect, who was not identified, was charged with "participation in the activities of a terrorist group and a terrorist attack," referring to the November 13 attacks in Paris.
Authorities had charged three others with similar offenses last week. The other 15 people detained on Sunday evening were released.
Meanwhile, French police say that an explosive belt — a without detonator — has been found in the southern Paris suburb of Montrouge. A police official says the belt was found by a street cleaner on Monday in a pile of rubble.
Police are currently analyzing the belt to see if it may have been used in the November 13 Paris attacks that killed 130 people, an official for the judicial police said. He could not be named because he was not authorized to discuss the investigation.
French jets bomb Iraq targets
Also on Monday, French jets from the Charles de Gaulle aircraft carrier struck Islamic State targets in Iraq while Britain offered France the use of an air base in Cyprus to hit the militants behind the Paris attacks.
French President Francois Hollande met British Prime Minister David Cameron in Paris on Monday as part of efforts to rally support for the fight against Islamic State and Hollande is also due to visit Washington and Moscow this week.
Cameron offered air-to-air refueling services and said he was convinced Britain should carry out air strikes alongside France and would be recommending that Britain's parliament vote through such measures.
France has intensified its bombings in Syria since the November 13 attacks in Paris claimed by Islamic State that killed 130 people. The group is also being targeted from the air by a U.S.-led coalition and Russia.
French jets taking off from the country's flagship in the eastern Mediterranean destroyed targets in Ramadi and Mosul in Iraq on Monday in support of Iraqi forces on the ground, the French armed forces said in a statement.
The arrival of the Charles de Gaulle aircraft carrier in the area following the Paris attacks has tripled the French air force's firepower by boosting the number of planes targeting Islamic State to 38.
"I firmly support the action that President Hollande has taken to strike ISIL (Islamic State) in Syria and it is my firm conviction that Britain should do so too," Cameron said at a joint news conference after his meeting with Hollande.
"Later this week, I will set out in parliament our comprehensive strategy for tackling ISIL," Cameron said.
Cameron is eager to avoid a repeat of 2013 when he lost a vote on air strikes against Syrian President Bashar al-Assad's forces. Britain is already bombing Islamic State in Iraq.
Hollande said France planned to intensify its air strikes on Islamic State in Syria, adding that it would focus on destroying targets that would cause as much damage as possible.
Besides the aircraft carrier, Britain's Cyprus Akrotiri air base could offer another option for French jets, which had been using bases in Jordan and the United Arab Emirates until Monday.
On Tuesday, Hollande is due to visit Washington where he hopes to overcome President Barack Obama's reluctance to get sucked further into the Syria conflict.
Speaking before Hollande's Washington trip, which will be followed by a visit to Russia later in the week, French officials made no secret of their desire to see the United States do more.