An international media watchdog has criticised a UAE court decision to uphold a 10-month jail sentence for a user of microblogging website Twitter who posted about the trial of 94 Islamists.

Reporters Without Borders (RSF) also called for the immediate release of another man it said was arrested in the United Arab Emirates this month on similar charges.

RSF "expresses outrage at the Abu Dhabi appeals court confirmation of the 10-month prison sentence of netizen Abdullah al-Hadidi," it said in a statement issued on Wednesday.

Hadidi is the son of one of 94 Islamists being tried in the Gulf state's top court over an alleged plot to seize power.

A court jailed him for posting details about the trials "with malicious intent", according to an activist.

Security forces arrested Hadidi on March 21 for publishing "in bad faith false details of the public trial session via the Internet," Amnesty International had reported.

The appeals court confirmed the sentence on Wednesday.

Another man, Waleed al-Shehhi, was arrested on May 11 over similar charges after he published "on his Twitter account information on the trial of 94 UAE citizens," RSF said.

Authorities held Shehhi in secret detention for a week.

"Reporters Without Borders calls attention to the fact that this netizen did nothing more than use social networks to provide relevant public information," it said.

It called "for him to be freed immediately and for the charges against him be dropped."

Authorities have only allowed some relatives of the 94 defendants, local journalists and human rights groups to attend the trial at the country's top security court.

The court will deliver its verdict in their case on July 2.

Prosecutors say the accused are linked to the Al-Islah group, which has ties to the Muslim Brotherhood.

Their trial is the largest in the history of the UAE, which has not seen any of the widespread pro-reform protests that have swept other Arab states, although authorities have cracked down on dissent and calls for democratic reform.