Some 30 to 40 suspected Islamic State jihadists who supported the November terrorist attacks in Paris are still at large, European authorities told CNN on Friday.
Officials warned of a heightened terror threat against the West as ISIS continues to face substantial losses in Syria, Iraq, and Libya.
"The outlook is as bleak as it has ever been," said Paul Cruickshank, editor of CTC Sentinel, a publication by the Combating Terrorism Center at the West Point military academy. "We’re talking beyond severe concern."
European nations involved in U.S.-led coalition strikes against ISIS face a greater risk of being targeted. Those include France, Belgium, the United Kingdom, the Netherlands, Denmark, and Germany.
Terror analysts warned that the United States is also vulnerable.
"It is by no means immune," Matthew Henman, editor of the U.K.-based IHS Jane’s Terrorism and Insurgency Center, told CNN.
He noted that the U.S.-Mexican border "is far from secure or impenetrable."
Airports are also susceptible to penetration as Western European passport holders can travel to the U.S. without a visa. U.S. nationals are also able to travel to and from Syria by flying into Western Europe and then departing from Turkey.
As of July, ISIS had lost a quarter of its territory over the past year. In retaliation, the terrorist group has ramped up its propaganda aimed at inspiring lone wolf attacks abroad.
Henman said the group will likely attempt to "inspire and provoke" repeat attacks similar to the December shooting in San Bernardino, California and the June massacre on a gay nightclub in Orland, Florida in the upcoming months.