BEIRUT » The video was undeniably silly: a 20-minute mockumentary about a fictional martial arts school in Dubai, where grandmaster "Saloom Snake" trains combatants to throw sandals, strike with the thin ropes of an Arab headdress and summon help on Twitter for fights that never actually occur.

But the authorities in the United Arab Emirates were not amused. In April, the police arrested five men who had participated in the video, including a U.S. citizen, Shezanne Cassim, 29, and threw them into jail, where they have been awaiting trial for eight months on charges of threatening national security.

The case has worried U.S. officials and baffled the defendants’ families, who say the video merely pokes fun at Emirati youth who imitate foreign films and rap videos. But the men have faced a legal process set up for grave crimes.

Rights groups say the case is only the most recent example of the extreme sensitivity of Gulf monarchies to the power of social media as a forum for critical — and uncontrollable — social and political discourse. Satire, especially political satire spread on social media, is treated as subversive. A number of Gulf countries have laws against cybercrimes, and in recent years a string of people have been jailed for content posted online.

But the case is also the latest instance of foreigners in Dubai — a city of extremes, with hard-partying clubs and conservative Emirati norms — getting entangled in the legal system for acts that might seem ordinary in the West, like public drinking or kissing.

In July, after a video showing an Emirati man hitting an Indian van driver went viral, the police arrested the Emirati as well as the man who had posted the video because he had "shared" images of a potential crime.

The case over the martial arts video is likely to embarrass the UAE at a time when the country is advertising itself as an international destination for culture. Last week, Dubai won the bid to host the World Expo in 2020 under the slogan "Connecting Minds, Creating the Future," after a lengthy campaign endorsed by Bill Gates.

Sheikh Mohammed bin Rashid al-Maktoum, the ruler of Dubai, said on Twitter that the Expo "would breathe new life into the ancient role of the Middle East as a melting pot for cultures and creativity."

On Friday, the Dubai International Film Festival begins, with Cate Blanchett and Martin Sheen among the guests. Critics say that jailing residents for online expression contradicts that message of openness.

"Dubai’s business model relies on it being able to project an image of progressiveness and stability, and hosting expos and film festivals all fits into this," said Nicholas McGeehan, Gulf researcher for Human Rights Watch. "But cases likes this seriously undermine that image and reveal it to be nothing more than a public relations artifice."

Emirati officials did not respond to requests for comment.

The case has only become public recently, after the family of Cassim, the U.S. citizen, decided that their efforts to navigate the Emirati justice system had done them little good.

"There seems to be no end in sight," said Cassim’s brother, Shervon, who spent nearly three months in the Emirates trying to secure his brother’s release.

In a telephone interview from his home in North Carolina, Cassim said his brother’s detention had become a bitter end to his family’s decades-old relationship with the Emirates.

His parents emigrated from Sri Lanka to Dubai in 1976 because it was a land of opportunity "where you could go and make your fortune," he said.

His mother worked for an airline and his father became an advertising executive, part of the large group of expatriates that helped expand the city from a desert backwater into the hypermodern crop of skyscrapers, malls and upscale hotels that it is today.

Shezanne Cassim’s two siblings were born there, and all three were educated in British private schools, where they had close friends from the Emirates and many other countries, his brother said.

"We were so happy to see Dubai boom and we have so much affection for the city and its people, and yet this is how the authorities treat my brother," he said.

The family moved to the United States in the early 2000s and became citizens. But Shezanne Cassim returned to Dubai after graduating from the University of Minnesota in 2006 to do business development for a subsidiary of Emirates airline, his brother said.

Three weeks before his arrest, he had started a consulting job with PricewaterhouseCoopers.

In his free time, Cassim and his friends made videos spoofing aspects of Dubai life. The videos start with a "Don’t try this at home" warning, then show Cassim doing things he says are not done in Dubai, like changing lanes on the highway to let faster drivers pass and cleaning up after yourself at McDonalds.

In one video, he wears deodorant on the metro, implying that other riders don’t.

In October 2012, the martial arts mockumentary was posted online, in which a portly "grand master" in a striped robe explains the UAE’s key weapons: the sandal, the rope from an Arab headdress and "the Twitter."

In April, after the video had logged thousands of views, the police detained Cassim and four others who appear in the video. They were later put on trial for national security violations that include endangering public order.

Emirati commentators, none of whom wanted to be named in connection with a national security case, guessed that the authorities objected to the video’s stereotyping of Emiratis or thought it implied that the country had gangs. One suggested that the police had cracked down to prevent a "snowball effect" of similar videos in the future.

The case recalls the fate of the Sudanese rapper Dangour, who was arrested in the Emirates in June 2011 and jailed for two years after he posted a video of himself rapping about drugs and violence.

But not all such indiscretions are punished. One month before Dangour’s arrest, the Emirates welcomed the American rapper Snoop Dogg, who greeted the audience in a white robe and Arab headdress to deliver an expletive-filled show.

The verdict in Cassim’s case was expected in September, but it has been delayed numerous times. His family said that he was being held in a desert prison outside Abu Dhabi with the other four defendants and that he had not been allowed to meet privately with his defense lawyer.

A State Department official said that the United States was "troubled by the prolonged incarceration" of Cassim and that U.S. diplomats were working with their counterparts in the UAE to "to urge a far and expedient trial and judgment."

Cassim’s next hearing is scheduled for Dec. 16.

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Ben Hubbard, New York Times