A Tunisian court has sentenced three European feminist activists to four months in jail after they demonstrated topless in central Tunis last month against the Islamist-led government, one of their lawyers said.

Marguerite Stern and Pauline Hillier of France and Josephine Markmann of Germany, all members of the Femen protest group, appeared topless on May 29 to call for the release of fellow activist, Tunisian Amina Tyler, who was detained last month.

"The judge sentenced the three Femen activists to four months and one day in prison for an attack on public morals and indecency," said one of their lawyers, Souheib Bahri.

Tyler, 18, was arrested in Kairouan on May 19 after she hung a feminist banner from the wall of a mosque and tried to bare her breasts, on the same day that the Islamist Ansar al-Sharia group held a rally in the city that authorities tried to ban.

She remains in custody awaiting trial.

Tyler has been at the centre of controversy in recent months after she published topless photographs of herself on Facebook with the words "My body belongs to me and not the honour of others" written on her chest in Arabic.

French Foreign Minister Laurent Fabius asked the Tunisian judiciary last week to show leniency towards the Femen activists.

"There are laws to be respected, but their act does not require major punishment," Fabius told French radio station Europe 1.

Tunisia was the first country to be rocked by an "Arab Spring" uprising, inspiring similar revolutions in Egypt and Libya.

The new government is led by a moderate Islamist party, Ennahda, but hardline Islamist Salafists are seeking a broader role for religion, alarming a secular elite which fears this could undermine individual freedoms, women's rights and democracy.