Twitter briefly suspended the account of David Duke, a white supremacist and former Imperial Wizard of the Ku Klux Klan on Monday (6 March). For a few hours, users who tried viewing the onetime Louisiana state representative's tweets were met with a message saying his account was suspended.

The platform reinstated his account after a few hours. Duke later tweeted saying he did not know why he was suspended.

"I'm back," Duke tweeted. "Though I have no idea why I was suspended. Thank you to all of the wonderful people who offered support. #FreeDavidDuke."

"True political dissent is always controversial," he wrote in a separate tweet. "Freedom of speech is always paramount. Thank you all for your huge wave of support for free speech."

According to BuzzFeed News, Duke's suspension was a mistake after an agent accidentally marked his account for suspension during a routine account review. Twitter quickly worked to restore the account after word of his suspension began to spread.

"We regularly review accounts and take action if they are found to have violated Twitter's rules," the spokesperson said in a statement. "If an account is found to have been suspended in error, we immediately restore it and notify the owner of our mistake."

Before the suspension, Duke's account had more than 30,000 followers. However, after it was restored, his follower count dropped to under 100 followers before eventually returning to its original count after a few hours.

"Never had my account verified, though everyone knows this account is mine," he wrote. "Hopefully one day I'll get the blue check."

Many Twitter users questioned Twitter's decision to reinstate Duke's account on the platform, adding to mounting criticism that the company is not doing enough to deal with its harassment problem.

In February, Duke lashed out at Avengers star Chris Evans on Twitter saying, "Why does Chris Evans, who plays the Jewish inspired super hero, Captain America, hate the women of his people so much? #WhiteGenocide." Duke posted the message along with a photo of Evans with ex-girlfriend Jenny Slate, Moonlight star Naomie Harris and Guardians Of The Galaxy actress Zoe Saldana.

A few days prior, Evans criticised the Senate's confirmation of Jeff Sessions as attorney general and suggested that David Duke's support of Sessions was enough to disqualify him.

Evans, however, quickly hit back at Duke's personal attack.

The brief suspension comes as Twitter struggles to crack down on hate speech, online harassment and abuse on its platform.

Last week, the social media company rolled out new measures to detect and curb harassment on Twitter in its latest safety update by expanding its mute and filter features. If Twitter's algorithm detects abusive behaviour, it will also limit the harasser's account for a set time period in a new "time out" feature that allows only their followers to see their posts.

In December 2016, Twitter suspended a number of high-profile alt-right users including that of Richard Spencer, head of the National Policy Institute. Spencer's account was eventually restored. Last summer, the platform permanently banned former Breitbart editor Milo Yiannopoulos for allegedly instigating a barrage of vicious vitriol targeting actress Leslie Jones.

Spencer slammed Twitter for Duke's brief suspension and called on people to fund a lawsuit against Twitter for discrimination.