A Tunisian rapper jailed for two years for a song in which he insulted the police will be freed on appeal, to the relief of his supporters who hailed Tuesday's ruling as a victory for freedom of expression.

Ala Yaacoubi, who goes by the rap name Weld El 15, was imprisoned on June 13 for a song he wrote called "The Police are Dogs," and the Tunis court of appeal on Tuesday reduced the jail term to a six-month suspended sentence, allowing him to go free.

"It's a victory for freedom and democracy, for Weld El 15 who did nothing wrong but made a work of art," attorney Ghazi Mrabet, who used the singer's rap name, said following the court's verdict.

As the ruling was announced, shouts of joy erupted outside of the court of appeal in Tunis where friends and supporters of the rapper had gathered.

"Freedom for Weld El 15!" they shouted.

"After being shaken by a great wave of concern, today's verdict is a relief for us. It has given reassurance," said Thameur Mekki, who heads the rapper's support group.

The 25-year-old musician was to be freed from the prison in a suburb of the capital where he has been held since his conviction by the court of first instance last month.

The severity of the two-year jail sentence infuriated his supporters who attended the trial, and clashes with the police broke out afterwards in which some of them were badly beaten.

Two rappers and a French-Tunisian journalist implicated in the violence were later charged with abusing public officials in the course of duty and attacks on public morals, and are due to stand trial in October.

The initial jail sentence was sharply criticised even by some government officials. Members of the opposition and human rights groups called it an attack on freedom of speech, a charge rejected by Islamist Prime Minister Ali Larayedh.

"He was not tried on the basis of his work, or the freedom of expression, but for inciting hatred and calling for the death of police and magistrates," Larayedh said on Monday, in an interview with television channel France 24.

In a video of the song which was posted on YouTube, the rapper is heard saying: "Police, magistrates, I'm here to tell you one thing, you dogs; I'll kill police instead of sheep; Give me a gun I'll shoot them."

The decision to release Yaacoubi comes less than a week after three European women with radical topless protest group Femen walked free when their four month jail sentences for baring their breasts in Tunis were also suspended on appeal.

Tunisia's Islamist-led government has frequently been accused by its critics of seeking to curb civil liberties acquired after the popular uprising that overthrew former strongman Zine El Abidine Ben Ali in January 2011.

In March 2012, two young graduates, both atheist, were sentenced to more than seven years for publishing caricatures of the Prophet Mohammed on Facebook.

And Amina Sboui, a Tunisian activist with the topless protest group, was arrested in May for painting the word "Femen" on a wall near a cemetery in the city of Kairouan, in protest against a planned gathering of Salafists.

She remains in custody waiting to hear whether she will be prosecuted for desecrating a cemetery and indecency, which carry prison terms of two years and six months respectively.

Rights activists have written an open letter to French President Francois Hollande, who is expected in Tunis later this week, asking him to raise the most pressing human rights issues during his visit.