By Yasmeen Abutaleb and Dustin Volz

SAN FRANCISCO (Reuters) - Twitter Inc <TWTR.N> late on Tuesday permanently suspended a number of user accounts for harassment, vowing to redouble its efforts to quickly thwart abusive behavior and block repeat offenders from the social media site.

The move appeared to be a response to abuse and harassment that Ghostbusters actor Leslie Jones, who is black, said on Monday had become so severe that she was quitting the service.

Among those banned was Breitbart tech editor Milo Yiannopoulos, a conservative who has been a provocative figure on Twitter for years and was accused by Jones and other Twitter users of feeding the abuse.

After Jones blocked him on Twitter, Yiannopoulos tweeted a screenshot of her page and wrote, "rejected by yet another black dude." He also was accused of sharing racist tweets from an account purported to belong to Jones, according to screenshots in news articles.

His tweets have since been deleted from Twitter.

Yiannopoulos did not respond to Reuters' requests for comment.

In a CNBC interview on Wednesday, he denied sending sexist or racist tweets to Jones, and said the only "proof" was that he teased the actress on Twitter because he didn't like her movie. He added that he was not responsible for other people's tweets.

Jones retweeted and shared several tweets disparaging her race and gender that she received on Monday before telling her 250,000 followers, "I leave Twitter tonight with tears and a very sad heart. All this cause I did a movie. You can hate the movie but the shit I got today ... wrong."

RIGHT BALANCE

Twitter, long criticized for not doing enough to police abusive behavior on the often-freewheeling messaging service, has struggled to find the right balance between free expression and blocking violent or hateful speech.

Mary Anne Franks, a law professor at the University of Miami who helps run the Cyber Civil Rights Initiative, said the new suspensions were "a sign that Twitter is trying to get a handle on what has clearly been a problem on the platform for the last few years."

Other celebrities have taken issue with what they view as abuse on the site, including writer and actress Lena Dunham, who said in September that she had hired someone to tweet on her behalf because it was no longer a "safe space" for her.

Twitter said in a statement on Tuesday that it had seen an "uptick" in the number of accounts violating its abuse and harassment policies over the past 48 hours, and had enforced its policies by issuing warnings or permanently suspending users.

"We know many people believe we have not done enough to curb this type of behavior on Twitter. We agree," Twitter said in the statement. "We are continuing to invest heavily in improving our tools and enforcement systems to better allow us to identify and take faster action on abuse as it's happening and prevent repeat offenders."

Twitter did not elaborate on what those efforts entailed.

Tuesday's account suspensions prompted scores of users to accuse the company of doling out suspensions inconsistently, with a bias against conservatives, including Yiannopoulos. The hashtag #FreeMilo was trending on Twitter on Wednesday.

"According to Twitter Milo is bad, Ayatollah [Ali] Khamenei, who regularly calls for another Holocaust, less bad. #FreeMilo" tweeted political talk show host Dave Rubin, referencing Iran's Supreme Leader.

Jones, who is a regular cast member on NBC's "Saturday Night Live," tweeted that she understood that Twitter needed to accommodate free speech but added that there needed to be some guidelines.

Some of the tweets targeting Jones compared her to an ape. User YellowArmedImposter wrote, "Your Ghostbusters isn't the first to have an ape in it," which Jones shared with the comment: "I just don't understand."

"I used to wonder why some celebs don't have Twitter accts now I know," she wrote in another tweet.

(Reporting by Yasmeen Abutaleb in San Francisco and Dustin Volz in Washington; Editing by Jonathan Weber, Nick Macfie and Paul Simao)