WASHINGTON—U.S. President Donald Trump’s Twitter account was deactivated for 11 minutes Thursday night by a company employee on the last day on the job, Twitter said, raising serious questions about the security of a tool the president uses to set major policy agendas, aggressively go after his critics, and connect with his core voter base.

The company has suspended other high-profile accounts in the past for violating its terms and conditions. It has also faced questions over why it has not previously suspended Trump’s Twitter account for violating its terms of service — a decision it defended by saying Trump’s position means his messages meet a higher standard for “newsworthiness.”

But there has not been a case where an employee has acted alone to take down the account of a well-known person, seemingly on their own.

The president is aware of the issue and the White House is in touch with Twitter, said an official who spoke on the condition of anonymity to discuss a delicate matter.

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Twitter initially posted a statement Thursday night saying Trump’s “account was inadvertently deactivated due to human error by a Twitter employee.”

For those few minutes, visitors to Trump’s account were simply met with the message, “Sorry, that page doesn’t exist!”

“The account was down for 11 minutes, and has since been restored,” the statement read. “We are continuing to investigate and are taking steps to prevent this from happening again.”

Two hours later, Twitter updated its statement, saying an investigation showed the deactivation “was done by a Twitter customer support employee who did this on the employee’s last day.” Twitter said it would be conducting a full internal review.

Trump has used the account since March 2009. He has tweeted more than 36,000 times and has 41.7 million followers.

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Trump has spoken publicly about his reliance on Twitter before. In an interview with Maria Bartiromo of Fox Business Network last month, Trump credited his use of social media as among the reasons he was elected.

“You have to keep people interested also,” he said. “You know, you have to keep people interested.”

Twitter also serves as among Trump’s main tools for deflecting criticisms and attacks. In the same interview, Trump said, “When somebody says something about me, I am able to go bing, bing, bing and I take care of it.”

Trump conceded that those close to him try to steer him away from social media. But he insists on tweeting — spelling errors included — as a weapon against “fake news.”

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