Alwaght-Belgian authorities believe more ISIS terrorists have been dispatched to Europe following last month's deadly terrorist attack in the country's capital, Brussels.
A spokesman for the country's crisis center said: "There are indications that ISIS has sent fighters to Europe and Belgium, the threat level which is currently at three will not go down."
The warning comes as it was reported ISIS terrorists planning to target European resorts this summer in a similar fashion to last year's beach massacre in Tunisia.
German newspaper Bild said German intelligence have been told of the plans by their Italian counterparts, who were in turn informed by a "credible source" in Africa.
According to the report, the terrorists plan to pose as beach vendors and detonate bombs hidden under sun loungers, before opening fire with automatic weapons.
Earlier on Tuesday, Spanish police announced they had arrested a Moroccan man on the island resort of Palma de Mallorca who was suspected of recruiting fighters for ISIS
A police statement said: "The accused had close contact with established terrorists involved with Daesh (Arabic acronym for ISIS) who are currently located in Syria."
Last year, Spain raised its anti-terror alert level to four out of a possible five.
Meanwhile, the head of the European Union's security agency says he's "not entirely confident" all those involved in the deadly Brussels and Paris attacks have been arrested.
"That's because we have a fragmented intelligence picture of precisely who is involved and where they are," Europol's Director Rob Wainwright said.
He added that he was "certainly not confident" other militant cells are not planning another attack in Europe.
The Paris attack in November left 130 dead and many others injured.
Last month, one of those believed to be responsible for the attack - Salah Abdeslam - was caught alive in Brussels following a four-month manhunt.
In June 2015, a gunman allegedly linked to ISIS opened fire on the beach at the popular Tunisian resort area of Sousse. At least 38 people were killed and dozens injured in the attack. Sousse attracts tourists from Europe as well as neighboring countries.
In March 2015, an ISIS-staged attack on the Bardo Museum in Tunisia’s capital, Tunis, claimed at least 22 lives. The attackers had massive bombs strapped to their bodies.
In mid-March this year, terrorists killed at least 16 people, including four Europeans, after they opened fire near several hotels in the Ivory Coast.
Al Qaeda affiliate in North Africa, the terrorist outfit that struck hotels in Mali in November last year and Burkina Faso in January this year, claimed responsibility for the assault, saying that three attackers were involved.
