A complaint of incitement to violence has been filed by one Jewish activist against another following a message posted on the social-networking site Facebook.

After Doron Isaacs, a former head of Habonim, co-organised the visit of 23 prominent South African human-rights activists to Israel and the West Bank at the beginning of July, a Facebook group was set up titled "Stop Doron Isaacs and Habonim".

On August 15, Ze'ev Krein, an administrator of the group, posted a message warning Mr Isaacs that "if you ever try anything against my beautiful Peaople (sic) and Land again you will see my foot on your head".

Approached for comment, Mr Krein, 27, a forensic scientist with the South African Police Service, said his comments were "obviously coming from emotion" and that it was "ridiculous" for him to be accused of incitement to violence.

"I'm venting my anger on this website - obviously in no way did I mean to do anything physically to him," he said. "The point of the site is to bring awareness to the Jewish community that what he's doing cannot be condoned."

Mr Isaacs, the coordinator of an educational charity, said it was "silly" to attack Habonim for his activities because he had not been a member of the movement for five years. Nevertheless, the left-wing Zionist youth movement had taught him "to be truthful, to stand up for justice and not to be silent about one's convictions".

He said the Facebook group was based on the belief that "one 27-year-old masterminded and hoodwinked 22 of the most experienced people in the country into believing false things and having a warped perspective on Israel-Palestine, which is ridiculous".

Mr Isaacs's colleague Nathan Geffen, who laid the complaint against Mr Krein, said he had done so because "we must be very clear that free speech does not include threats of violence".

Police will now carry out a preliminary investigation and the director of public prosecutions will then consider whether or not to prosecute.