- The four suspects allegedly joined ISIS in Syria "to commit terrorist acts"
- They were arrested in the Copenhagen metropolitan area, police say
- Authorities seized weapons and ammunition in connection with the arrests
Copenhagen police and Denmark's security and intelligence service, known as PET, worked together to make the arrests in the Copenhagen metropolitan area, according to a police statement.
Copenhagen police spokesman Mads Jensen told CNN that authorities found weapons and bullets in a related search. But it was not immediately clear the amount discovered, or whether the suspects were actively plotting a terrorist attack.
Copenhagen police declined "for the sake of further investigation" to specify what led to the arrests or the identities of those detained, even their genders and nationalities.
The four are suspected of having enlisted with ISIS in Syria, which has become a magnet for would-be jihadists.
They are accused of having joined the group in Syria "to commit terrorist acts," according to police. The four are set to appear in closed-door hearings Friday.
Fears of more attacks in Europe
The infiltration of armed ISIS militants in Europe has become a big worry after deadly attacks in Brussels, Belgium,
in March and Paris
in November. The terror group has claimed responsibility for both those attacks.
After Brussels, officials said dozens of potential and known ISIS operatives were planning fresh attacks
around Europe. Electronic intercepts, human sources and database tracking suggested that several targets had been picked out since 130 people died in the November 13 shootings and bombings in the French capital, according to U.S. counterterrorism officials.
The self-proclaimed Islamic State has conducted or inspired terrorist attacks in 20 countries other than Iraq and Syria
. Some attackers have taken direct or indirect orders from ISIS higher-ups. Others have been inspired by the group's leaders, approach and philosophy, which generally calls for war against any who don't subscribe to its violent, radical Islamist ideology.
The latter appears to be what happened in Denmark in February 2015. A man who swore fidelity to ISIS leader Abu Bakr al-Baghdadi in a Facebook post attacked a free speech forum
featuring a controversial Swedish artist and then fired shots near a synagogue in Copenhagen.
Two civilians were killed and five police officers wounded, according to Danish authorities.
Police tracked down the gunman and shot him dead. Authorities identified him as a 22-year-old man born in Denmark who'd been "well-known by the police for several criminal incidents."