European feminist activists who spent a month in jail after a topless protest in Tunisia retracted the apology they made a day earlier to go free and claimed to have endured filthy and humiliating conditions in prison.

The two French women and a German member of the Ukrainian group Femen were freed overnight after a court in the Muslim country lifted their prison sentence. Hours later, on Thursday, they arrived in France.

The women, who were convicted for taking off their shirts outside a courthouse in the capital, Tunis, maintained during the trial that there was nothing sexual or offensive about their protest and that it was only to support an imprisoned Tunisian colleague.

All three apologised on Wednesday during their appeals hearing. But , they held up clenched fists on their arrival at Paris' Orly airport and retracted those remarks.

"We regret nothing. Femen never regrets its actions," Frenchwoman Pauline Hillier said at a news conference. She said the women were told that if they did not express regret, they would have to serve the full four months they were sentenced to for public indecency, offending public morals and threatening public order.

The protest was the first of its kind in the Muslim world for Femen, which has used nudity to push for greater rights for women across Europe.

The women described what they said were horrendous conditions during their month in custody in Tunis. They claimed the jail was filthy, with blood stains on the floors, and that they slept under urine-soaked covers and mostly cleaned themselves with toilet water. They also described regular strip searches, when they were sometimes slapped.

"Religious tyranny is everywhere, including in prison," Hillier said. "The only book allowed for prisoners is the Qur'an. The only activity proposed to the prisoners is religious instruction. (There were) prayers on television every day."

Tunisians overthrew their secular dictator in 2011, kicking off uprisings across the Arab world. In the ensuing years, however, there has been a rise in conservative Islamist movements at odds with Tunisia's longstanding image as secular and progressive – especially in regard to women's rights.

The Femen activists were calling for the release of Amina Sboui, a Tunisian member of Femen who scandalised the country in March by posting topless photos of herself as a protest. She later attempted another protest on 19 May in the religious centre of Kairouan, where she was arrested.

Sboui, who has also used the pseudonym Amina Tyler, has already been fined for carrying pepper spray.