An MP has reported abusive messages from online trolls saying they hope she gets raped to police.
Cat Smith, Labour MP for Lancaster and Fleetwood, said Facebook told her the messages did not breach its "community standards".
She tweeted that one of the messages said she "should be raped by 100 Muslims" and said another troll posted: "Hope she gets raped then."
Facebook said it has removed them and not doing it initially was a "mistake".
The social media site said in a statement: "These posts, which violate our policies, have now been removed.
"We apologise for our mistake in not removing them when first reported to us and any distress caused.
"We have a comprehensive reporting system in place and our teams work around the clock to review content reported by our community but sometimes they do make mistakes."
Facebook added it was taking on 3,000 more reviewers to improve response to these reports and continued to work closely with safety experts including The Internet Watch Foundation.
Ms Smith, who was elected in May 2015, said she reported the messages on 9 September.
She currently serves as a shadow cabinet minister for Voter Engagement and Youth Affairs and is shadow deputy leader of the House of Commons.
Lancashire Police said it was investigating offensive messages on social media.