BEIJING — Beijing organizers have staged a full dress rehearsal of next month's Olympics opening ceremony under strict secrecy, state media reported today.

A rundown of the 3 1/2-hour event was held overnight Thursday at the newly built National Stadium, with security guards manning three concentric rings of checkpoints, the official Xinhua News Agency reported.

Participants and stadium workers were required to sign confidentiality agreements, the report said without mentioning if problems were encountered.

The event is being directed by celebrated Chinese film director Zhang Yimou, who has spent the last three years designing the spectacle alongside a creative team of international artists and event planners.

Last minute changes include the addition of a tribute to rescuers and victims of the May 12 earthquake in southwestern China's Sichuan province in which almost 70,000 people perished. Three more rehearsals are planned ahead of the games' Aug. 8 opening, the report said.