PARIS (AFP) - Charlie Hebdo's chief editor said a Turkish version of the satirical French magazine will be sold on Wednesday because constitutional secularity is "under attack" in mainly Muslim Turkey.

The issue will appear as a four-page insert in the centre-left opposition daily Cumhuriyet, one of the Turkish paper's journalists told AFP, requesting anonymity.

Gerard Biard of Charlie Hebdo told AFP on Tuesday that the Turkish version was "the most important" of the five foreign versions of the weekly being published a week after 12 people were killed in an attack on its Paris offices.

The special issue features a caricature of the Prophet Mohammed on its cover holding a "Je Suis Charlie" sign under the title "All Is Forgiven". Turkish media described the cover but did not reproduce it.

"Turkey is in a difficult period and secularity there is under attack," Biard said.

Cumhuriyet initially denied that it had reached an arrangement with Charlie Hebdo, telling AFP that such a deal was just a "rumour". But the anonymous journalist told AFP that the paper decided to reprint four pages of the edition after a long debate.

Turkish President Recep Tayyip Erdogan has in recent weeks come under strong pressure over freedom of the press in the country following raids in December against opposition media.

Turkey has long been accused of a lack of press freedom, and Erdogan of seeking to roll back the principle of secularity enshrined in Turkey's constitution.

Turkey, which once had large Christian minorities, is now 99 per cent Muslim, and critics of Erdogan's ruling Justice and Development Party (AKP) have accused it of trying to Islamise society.

The president, a practising Muslim, has described efforts to promote birth control as "treason", told young Muslims with tattoos to beg God for forgiveness, and called for a new school curriculum to give prominence to historical Muslim scholars.

Turkey was the world's top jailer of journalists in 2012 and 2013, ahead of Iran and China, according to the international Committee to Protect Journalists, before improving to 10th place in 2014.

The first issue of Charlie Hebdo since Islamist gunmen attacked it last week, killing 12 people, is to come out in six languages. The French, Turkish and Italian versions will be printed, while the English, Arabic and Spanish ones will be offered in electronic form.