Dutch police arrested 15 people, including four minors, on Tuesday for encouraging others online to commit acts of terrorism.

The suspects are aged 16 to 53 and the arrests took place nationwide, with most – four – carried out in The Hague. The alleged ringleader was arrested earlier on January 20.

The suspects were said to be active on TikTok and other social media channels, spreading propaganda linked to the terrorist organisation Islamic State. Three of the suspects have Dutch nationality and the rest are Syrian, the public prosecution department said in a statement.

The investigation began last year after police were alerted to a TikTok account showing IS propaganda with Dutch subtitles.

Some of the posts called on people to join the IS struggle, while others praised martyrdom. Some of the videos had been viewed more than 100,000 times.

The suspects face charges of inciting others to commit acts of terrorism, spreading IS propaganda and being members of a terrorist organisation. The public prosecution department said further arrests cannot be ruled out.