An amended lawsuit filed in federal court on Sunday alleges that rap moguls Jay-Z and Sean “Diddy” Combs raped a 13-year-old girl during a party in 2000.

Jay-Z denied the allegations on social media and lambasted the lawsuit, calling it part of a “blackmail attempt” by the plaintiff’s lawyer. Lawyers for Jay-Z did not immediately respond to a request for comment.

The lawsuit was filed originally in October in the Southern District of New York and at that time did not name Jay-Z as a defendant, though the amended lawsuit says that Jay-Z was identified as “Celebrity A” on the original complaint.

Combs denied all allegations against him, including this one, in October. He is in jail on federal sex trafficking charges, to which he has pleaded not guilty.

The lawsuit alleges that the unnamed girl was drugged and raped by both Jay-Z and Combs at a party hosted by Combs after the MTV Music Awards in 2000, which were held in New York.

Tony Buzbee, the Texas lawyer representing the girl who filed Sunday’s lawsuit, has filed at least 20 civil lawsuits against Combs accusing him of sexual misconduct.

In an email to Reuters, Buzbee said the Jay-Z lawsuit “speaks for itself”.

“This is a very serious matter that will be litigated in court,” Buzbee wrote.

Buzbee, in his amended lawsuit, says his law firm had previously sent Jay-Z a letter seeking to mediate a settlement.

Jay-Z, the lawsuit says, responded to that letter by filing a lawsuit against Buzbee, and by “orchestrating a conspiracy of harassment” against Buzbee and other lawyers in his firm, which the lawyer said was an intimidation tactic meant to silence his client.

In a post on social media, Buzbee said the alleged rape victim he was representing “never demanded a penny” from Jay-Z, writing that “she only sought a confidential mediation”.

Buzbee last week filed a lawsuit against the law firm Quinn Emanuel Urquhart & Sullivan, whose lawyers represent Combs and Jay-Z, accusing the firm’s legal team of harassing his colleagues, his clients and his family.

Quinn Emanuel Urquhart & Sullivan did not respond to requests for comment.