The trial of 94 Islamists accused of plotting against the United Arab Emirates began Monday in the absence of rights activists and foreign reporters, who according to witnesses were barred from the court.
The Federal Supreme Court, which also acts as state security court, convened in Abu Dhabi to try the activists arrested between March and December last year.
The accused are said by prosecutors to be linked to the Al-Islah group, which has ties with the outlawed Muslim Brotherhood.
UAE attorney general Salem Kobaish last month said the defendants would be tried for "having created and led a movement aimed at opposing the basic foundations on which the state's political system is built and at seizing power".
The group had formed a "secret organisation" which was in contact with individuals and organisations "abroad", including the Muslim Brotherhood, Kobaish said.
The attorney general said they had also created or invested in real estate companies to finance their organisation.
Relatives posted pictures on Twitter of representatives of human rights organisations standing outside the court building after allegedly being denied entry as observers.
Amnesty International said a Kuwaiti lawyer representing it as an observer was denied entry into the UAE.
"By denying access to observers from human rights groups, the UAE authorities are blatantly trying to manage what information is made available about the trial to the outside world," Amnesty International said.
The Kuwaiti lawyer, Ahmad Nashmi al-Dhafeeri, wrote on his Twitter account that he was sent back from the airport.
"I was prevented today from entering the UAE to monitor the trial of those accused of plotting to overthrow the government as a delegate for Amnesty International," Dhafeeri wrote on his Twitter account late Sunday.