Swiss prosecutors have charged an Ethiopian imam with inciting violence and other offences, they said on Friday, alleging he called in a mosque sermon for followers to kill Muslims who did not pray in the community.

The step by prosecutors in the northern town of Winterthur comes amid heightened sensitivity to the risk of Islamist violence in Switzerland, whose spy agency warned about the threat in May.

Prosecutors did not name the imam, one of four people they said were linked to the local An'Nur mosque and who have been under investigation since November on suspicion of inciting criminal or violent acts.

"In his homily of Oct. 21, 2016, in the An'Nur Mosque, he is accused among other things of calling for expelling Muslims who do not pray in the community, and even burning them and killing them in their homes if they still refuse," the prosecutors said in a statement.

He was also accused of sharing brutal depictions of killings via Facebook and of working as an imam without authorisation.

Prosecutors are seeking an 18-month suspended sentence and expulsion from Switzerland for 15 years for the cleric, who has been held in investigative custody since November.

Efforts to reach the mosque were not immediately successful. A number listed for the An'Nur cultural association that runs the mosque was no longer in service.

Swiss federal authorities say they have identified more than 500 internet users with Swiss connections who were using social media to spread jihadist ideas.

Concerns about militancy and potential attacks led Swiss voters to back a law last year extending the national spy service's authority to monitor internet traffic, deploy drones and hack foreign computer systems.

Switzerland has so far not been targeted directly in an Islamist attack, but it has had several links to attacks elsewhere in Europe last year.