Three men from Kosovo and an unidentified minor have been arrested in Venice on suspicion of plotting to blow up the city's celebrated Rialto Bridge, Italian police say.

The suspects were detained in an overnight sweep carried out after it was established that they had undergone “radicalization," according to a police statement.

Raids were conducted at 12 locations in the historic center of the city, which is a magnet for millions of visitors from around the world.

Adelchi d'Ippolito, the Venice prosecutor in charge of the case, said the suspects appeared to had been studying how to build explosives but did not have the necessary components for making a bomb.

He added that the suspects had talked about “unconditional support” for the Daesh terrorist group in a wiretapped conversation.

"There was a lot of talk about unconditional support to ISIS (Daesh). It wasn't just theory and dogma," D'Ippolito said of the wiretaps.

They were also envisioning moving on to "planning and projects," he added.

According to media reports, the wiretap evidence against the suspects also includes recordings of them celebrating the attack outside Parliament in London last week and discussing their desire to join terrorists in Syria.

The Rialto Bridge is the oldest of the four bridges that span Venice's Grand Canal, first built at the end of the 12th century.

(Source: AFP)