WASHINGTON — Twitter CEO Dick Costolo says he’s taking personal responsibility for the social media platform’s problems with harassment and abuse.

“I’m frankly ashamed of how poorly we’ve dealt with this issue,” wrote Costolo in an internal memo, obtained by The Verge.

Costolo said he is embarrassed by how slowly and ineffectively the company has dealt with “trolls” — people who anonymously post unpleasant, unseemingly, and often threatening content.

“I take PERSONAL responsibility for our failure to deal with this as a company,” wrote Costolo. “We suck at dealing with abuse and trolls on the platform and we’ve sucked at it for years.”

Costolo acknowledges the slowness to adopt tools to deal with harassment is hurting Twitter.

“It’s no secret and the rest of the world talks about it every day,” wrote Costolo. “We lose core user after core users by not addressing simple trolling issues that they face every day.”

Costolo says Twitter will get more aggressive with trolls.

“We’re going to start kicking these people off right and left and making sure that when they issue their  ridiculous attacks, nobody hears them,” wrote Costolo in the memo.

Robin Williams’ daughter Zelda left Twitter after abusive tweets following her father’s suicide. More recently, feminist critic Anita Sarkeesian was targeted because of her criticism of how women are portrayed in video games.

In December, Twitter released some tools to make it easier to flag abusive tweets and users.