US President Donald Trump's Twitter account briefly vanished on Thursday but has since been restored, the social media company said.
A customer service employee deactivated the @realdonaldtrump account, it said, clarifying that it had been their last day in the job.
The account was down for 11 minutes and Twitter is now investigating.
The president brushed off the outage in a new tweet on Friday, suggesting it showed the impact he was having.
My Twitter account was taken down for 11 minutes by a rogue employee. I guess the word must finally be getting out-and having an impact.— Donald J. Trump (@realDonaldTrump) November 3, 2017
Tweets from Mr Trump, who has 41.7 million followers, have frequently caused controversy.
The latest incident has sparked debate about the security of the president's account, given the potential consequences of posts falsely attributed to Mr Trump being published.
However, @POTUS, the official account of the US president, was unaffected.
On Thursday evening, visitors to Mr Trump's page for a short time could only see a message that read "Sorry, that page doesn't exist!"
After the account was restored, Mr Trump's first tweet was about the Republican Party's tax cuts plan.
Twitter said it was investigating the problem and taking steps to avoid it happening again.
On Thursday evening, the @TwitterGov account wrote: "Through our investigation we have learned that this was done by a Twitter customer support employee who did this on the employee's last day. We are conducting a full internal review."
Then on Friday, the San Francisco-based company posted: "We have implemented safeguards to prevent this from happening again.
"We won't be able to share all details about our internal investigation or updates to our security measures, but we take this seriously and our teams are on it."
Update: We have implemented safeguards to prevent this from happening again. We won’t be able to share all details about our internal investigation or updates to our security measures, but we take this seriously and our teams are on it. https://t.co/8EfEzHvB7p— Twitter Government (@TwitterGov) November 3, 2017
Through our investigation we have learned that this was done by a Twitter customer support employee who did this on the employee’s last day. We are conducting a full internal review. https://t.co/mlarOgiaRF— Twitter Government (@TwitterGov) November 3, 2017
'Bing, bing, bing'
Mr Trump joined Twitter in March 2009 and he has tweeted more than 36,000 times.
He has been actively using the social media platform to promote his policies and also attack his political opponents both during the presidential campaign in 2016 and since taking office in January.
In one interview he said that when someone said something about him, he was able to go "bing, bing, bing on Twitter" - and take care of it.
After he appeared to directly threaten North Korea with destruction in a tweet in September, Twitter was forced to justify allowing the post to stand.
Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won't be around much longer!— Donald J. Trump (@realDonaldTrump) September 24, 2017
It said that Mr Trump's tweet was "newsworthy".
In one of his other most controversial tweets, he taunted FBI chief James Comey days before sacking him in May.
James Comey better hope that there are no "tapes" of our conversations before he starts leaking to the press!— Donald J. Trump (@realDonaldTrump) May 12, 2017
Tweeting the following month, he admitted he had no such tapes of Mr Comey.
With all of the recently reported electronic surveillance, intercepts, unmasking and illegal leaking of information, I have no idea...— Donald J. Trump (@realDonaldTrump) June 22, 2017
...whether there are "tapes" or recordings of my conversations with James Comey, but I did not make, and do not have, any such recordings.— Donald J. Trump (@realDonaldTrump) June 22, 2017
Mr Trump's allies have also got into hot water over their use of Twitter.
Roger Stone, who advised him during his election campaign, was suspended from the network after he used abusive and homophobic language to target journalists, including a gay CNN presenter, Don Lemon.
He said he had been told by Twitter that he had violated its rules.
Mr Stone said he would sue Twitter for blocking his account.