In a statement issued on Saturday, the New York-based Committee to Protect Journalists, CPJ, expressed deep concern about the detention of Rabah al-Quwai, who works for the Okaz and Shams dailies and two Saudi-run websites.
Ann Cooper, the CPJ director, said: "We condemn the detention of Rabah al-Quwai and call for his immediate release."
The CPJ said Quwai was detained after criticising "the strict religious interpretations of hard-line Islamists who subscribe to the Wahabbi doctrine and who wield tremendous influence in the country".
Ouwai's lawyer said that his client was detained in the northern city of Hail on Monday after being summoned from Riyadh, with prosecutors reportedly questioning him for allegedly having "denigrated Islamic beliefs" in his articles.
"Saudi officials cannot say they support greater media reforms and then arrest journalists because of what they write"
Ann Cooper, CPJ director
The CPJ quoted Saudi media as saying Quwai had received threats in the past warning him to "go back to his religion and leave these fictions behind".
Despite some increased press freedoms since the attacks on the United States on September 11, 2001, Saudi authorities continue to crack down on critics.
"Saudi officials cannot say they support greater media reforms and then arrest journalists because of what they write," Cooper said.
The Committee to Protect Journalists