Two journalism advocacy groups have jointly written to Oman's sultan over the trial of three reporters and the shuttering of their newspaper.

The letter from the Committee to Protect Journalists and Reporters Without Borders, dated Wednesday, asks Sultan Qaboos bin Said for the "unconditional release" of the three reporters from the daily Arabic newspaper Azamn.

The letter says: "No journalist should be jailed for their reporting, regardless of the government's contentions concerning the veracity of their work."

The three are being tried over a story their newspaper published alleging improper interference in a court case. Oman's Information Ministry shut down their newspaper over the story.

The U.S.-based watchdog Freedom House considers Oman "not free," though it often serves as a diplomatic link between Western powers and Iran.