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Is it an act of violence or terror?
02:46 - Source: CNN

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The alert mentioned recent attacks in France, Russia, Sweden and the UK.

A US official told CNN that the terror threat in Europe was as high as it's ever been.

CNN  — 

The US State Department has issued a travel alert for its citizens going to Europe, citing the continued threat of terror attacks.

A Libyan traveller packs his laptop in his suitcase before boarding his flight for London at Tunis-Carthage International Airport on March 25, 2017. The United States this week announced a ban on all electronics larger than a standard smartphone on board direct flights out of eight countries across the Middle East, in effect from March 25, 2017. US officials would not specify how long the ban will last, but Emirates told AFP that it had been instructed to enforce the measures until at least October 14. Britain has also announced a parallel electronics ban targeting all flights out of Egypt, Turkey, Jordan, Saudi Arabia, Tunisia and Lebanon. / AFP PHOTO / FETHI BELAID (Photo credit should read FETHI BELAID/AFP/Getty Images)
A Libyan traveller packs his laptop in his suitcase before boarding his flight for London at Tunis-Carthage International Airport on March 25, 2017. The United States this week announced a ban on all electronics larger than a standard smartphone on board direct flights out of eight countries across the Middle East, in effect from March 25, 2017. US officials would not specify how long the ban will last, but Emirates told AFP that it had been instructed to enforce the measures until at least October 14. Britain has also announced a parallel electronics ban targeting all flights out of Egypt, Turkey, Jordan, Saudi Arabia, Tunisia and Lebanon. / AFP PHOTO / FETHI BELAID (Photo credit should read FETHI BELAID/AFP/Getty Images)
FETHI BELAID/AFP/Getty Images

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“While local governments continue counterterrorism operations, the Department nevertheless remains concerned about the potential for future terrorist attacks,” the alert said. “U.S. citizens should always be alert to the possibility that terrorist sympathizers or self-radicalized extremists may conduct attacks with little or no warning.”

The alert mentioned recent attacks in France – which heads to the polls next week to choose a new president – Russia, Sweden and the UK, noting that extremists tend to focus on tourist hot spots.

A US official told CNN in February that the terror threat in Europe was as high as it’s ever been.

Recent estimates from Europe and US say as many as 1,900 foreign fighters have returned to Europe after stints in Iraq and Syria, the official said. Some remain committed to terror groups like ISIS, but others returned disenchanted.

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The alert expires September 1.

CNN’s Barbara Starr and Laura Koran contributed to this report