The Muslim teenager arrested earlier this year when a teacher mistook his homemade clock for a bomb has threatened to sue his school and the Texas town of Irving for almost $21 million, his lawyer says.

Ahmed Mohamed, 14, became an overnight sensation in September after his sister tweeted a photo of the aspiring inventor standing in handcuffs while wearing a t-shirt with the US space agency NASA’s logo.

The Muslim teenager received an outpouring of public support after his arrest, including congratulations from Barack Obama on his skills and an invitation to take the clock to the White House in what was seen as a pointed rebuke to school and police officials amid accusations of Islamophobia.

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John M. Grunsfeld of the Science Mission Directorate poses with Ahmed Mohamed. Photo: ABC

Invitations also poured in from Facebook, Google and the United Nations, and Ahmed later tweeted photos of visits to Mecca, New York, Sudan and Qatar.

But his lawyer has insisted his fame brought with it “severe psychological trauma,” according to a letter notifying the city and school district of the demands.

The son of Sudanese immigrants who lived in a Dallas suburb, the young robotics fan brought in a homemade clock to impress a new teacher at MacArthur High School.

Instead, the teacher accused him of trying to scare people with a hoax bomb and police escorted him from the school in handcuffs.

His lawyers have insisted that the school, the police force and city officials violated Ahmed’s rights by wrongfully accusing and detaining him then “trashing” him when the media began reporting the story.

“Ahmed clearly was singled out because of his race, national origin and religion,” lawyer Kelly Hollingsworth said.

The letter said that Irving mayor, Beth Van Duyne, called the clock a “hoax bomb” during an appearance on a news and political opinion talk show The Glenn Beck Program.

The clock mistaken for a “hoax bomb”. Photo: ABC

Presenter Glenn Beck and his other guest also called the story “an influence operation” in furtherance of a coming “civilisation jihad”.

“Not only was this dangerous ‘baiting’ that destroyed any chance the Mohamed family ever had of being truly safe and secure in the US, but it was also defamatory,” his lawyers wrote.

The family received threatening emails and left their home after their address was publicised.

They eventually moved to Qatar after Ahmed was offered a generous scholarship.

His lawyers are seeking almost $7 million in damages from the school district and close to $14 million from the city of Irving, saying they will file a civil suit if they do not receive a reply within 60 days.