"We condemn these attacks and we hope that German and French authorities conduct swift, transparent and complete investigations that hold all of the perpetrators accountable," Anthony Mills, press freedom manager for the watchdog, said in a statement.

"We also reiterate that it is absolutely unacceptable to resort to violence against journalists to express political disagreement with them," it said.

The statement came a day after German police said that arsonists torched the headquarters of the Turkish-language newspaper Zaman in the western city of Cologne and attacked a cafe frequented by the Turkish community.

Authorities have not ruled out a link to the banned Kurdistan Workers' Party (PKK), considered by the European Union and Turkey as a terrorist organisation.

"In one of the two cases, we have evidence that a substance was used to spread the fire," the spokeswoman said. "Typical PKK slogans were shouted" during the two Cologne attacks.

On Wednesday, Zaman's offices in the Paris suburb of Pantin were vandalised by a dozen masked men, with a police source telling AFP that PKK had claimed the attack.

Zaman said that it marked the third attack against its Paris office in six months.

PKK activists have also previously attacked the newspaper's offices in London, Vienna and Zurich.

February 15 marked the 13th anniversary of the arrest of PKK chief Abdullah Ocalan.

The PKK took up arms in southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives. It is labelled a terrorist outfit by Ankara and much of the international community.