In an interview with the Tribune de Genève, Blerim Bunjaku, a socialist politician in the city and himself a Muslim, said the authorities were partly to blame for the rise of radical Islam in Winterthur, which has seen five young Muslims travel to the Middle East to fight for Isis.
“The authorities haven't done enough during the past few years to promote the integration of foreigners,” he said.
“Today, young Muslims grow up in Salafi families, cut off from Swiss culture. They see the West as an enemy.”
“The lack of reaction, or courage, of the authorities has let the problem get worse,” he added.
Last month police arrested a man suspected of being a key figure behind the radicalization of young Muslims in the area.
The man, known by the media only as S., has close links to the inner circle at Winterthur's An' Nur-Moschee mosque, broadcaster SRF said at the time.
“Though the majority of regulars there don't pose any problem, there are Isis sympathizers,” said Bunjaku.
Winterthur has taken steps in recent times to combat the conversion of young people to radical Islam.
In May it launched a new centre to provide a contact point for the public to report and discuss cases of extremism and violence.
The city has also offered training to teachers and youth workers to help them spot potential cases of radicalization.
But these steps are too little, too late, according to Bunjaku.
“Either [the authorities] have underestimated the problem, or they didn't want to see it,” he told the Tribune.
“Today the city still refuses to say that Winterthur is a Salafi hot spot.”
Bunjaku said there's no “miracle recipe” for combating radicalization but that better communication between the authorities and the Muslim community is essential, as well as prevention measures in schools and mosques such as religious education.
He also praised a report by the National Security Network, released earlier this week, which outlined ways cantons and communes could work at local level to combat the problem.