BERLIN — Austrian authorities said Sunday they had foiled a possible attack on Vienna’s Pride parade by three young men who had allegedly sympathized with the extremist Islamic State group.

The head of Austria’s domestic intelligence service told reporters that the suspects, aged 14, 17 and 20, were arrested before the start of Saturday’s Pride parade, which was attended by around 300,000 people, public broadcaster ORF reported.

Omar Haijawi-Pirchner from the State Protection and Intelligence Directorate said that there was “no danger for the participants of the parade at any time.”

Austrian Chancellor Karl Nehammer expressed his gratitude to the investigators for preventing “a possible Islamist attack in Vienna.”

“This shows once again that we must never give in in the fight against radicals and extremists,” Nehammer tweeted. “They are a threat to our democracy and security and must be dealt with severely.”

Vienna’s mayor expressed shock.

“There must be no place for hate and exclusion in Vienna. Our city is colorful and cosmopolitan,” Michael Ludwig said, according to Austrian news agency APA.

The intelligence service had received advance knowledge of the suspects’ alleged plans, kept them “under constant control,” and arrested them on the orders of the St. Poelten public prosecutor’s office following house searches on Saturday that uncovered various evidence, including weapons, ORF reported.

The three suspects, Austrian citizens of Bosnian and Chechen origin whose identities were not further revealed, had radicalized online and sympathized with the Islamic State group, Haijawi-Pirchner said.

One of the suspects was already known to police, he added.

The trio was arrested before the start of the parade by Austria’s Cobra special forces.

The organizers of the Pride parade were only informed about the events on Sunday, after the police raid had already taken place, ORF reported.

“We will not let the enemies of rights for LGBTQI people, democracy and an open society get us down,” the parade’s organizing team said, APA reported.

The rights of the community have recently been “increasingly threatened by backsliding and we have to fight every day for our visibility and safety,” said Ann-Sophie Otte, chairwoman of the Homosexual Initiative Vienna, according to APA.