Italian police on Thursday arrested three Kosovans in the lagoon city of Venice after one was caught on a phone intercept proposing they bomb the famed Rialto bridge while others lauded the recent attack in London. A minor was also detained.

Venice prosecutor Adelchi d’Ippolito said a search of a Venice apartment showed the suspects were getting in physical shape and watching videos of Islamic extremists demonstrating how to carry out knife attacks.

A phone intercept allegedly caught one of the suspects saying- “You’ll go straight to paradise because of all the infidels in Venice. Put a bomb on the Rialto.” It wasn’t clear if the reference was bluster or indicated an imminent threat.

Regardless, police said the bridge never was at risk because it is under constant surveillance.

The 16th century Rialto bridge, one of Venice’s iconic tourist draws, spans the Grand Canal and features small shops on either side of its stone steps.

Authorities identified the suspects as Fisnik Bekaj, Dake Haziraj and Arjan Babaj. They said the men talked about being ready to die for the jihadist cause and discussed being inspired by last week’s attack in London that killed four people.

Mr. D’Ippolito said the suspects were “truly dangerous” and were suspected of plotting attacks both in Italy and overseas. One had returned recently from Syria, he said. But he added that they wouldn’t have been able to carry out an attack in Italy since they were being closely watched.

Venice Police Chief Angelo Sanna said the detained minor made some of the most radical remarks.

“He was the most heated with his statements and declarations where he would crave for action,” Sanna said.

Italian police have made several arrests in recent years of suspected Islamic extremists, on allegations they were recruiting fighters for jihad in Syria and Iraq, were radicalizing others or were plotting attacks domestically.

Venice Mayor Luigi Brugnaro said all those detained had residency permits to live in Italy. He said police searched 12 sites in Venice’s center, Mestre, and nearby Treviso.