Image copyright Getty Images Image caption Dartmouth College is ranked as one of the top 20 US universities

Dartmouth College is facing a $70m (£54m) lawsuit from six women who claim the school ignored 16 years of sexual harassment by three ex-professors.

They allege the Ivy League school allowed the tenured psychology professors to harass, discriminate against and rape female students.

The federal lawsuit, filed on Thursday, names Dartmouth trustees as defendants, not the former professors.

The college denies the claims and will respond in court, a spokesman says.

What are the allegations?

The lawsuit says the elite school turned a blind eye to "bad behaviour by these professors for more than 16 years", having received many complaints about Professors Todd Heatherton, William Kelley and Paul Whalen.

The six named women, and a seventh Jane Doe, allege the professors had a clear bias towards hiring attractive young women to work in their labs and treated female students as "sex objects".

The three "predatory club" professors held meetings in bars, invited students to hot-tub parties, sent lewd photographs, groped and assaulted women, the plaintiffs say.

When students spurned their advances or refused to participate in their "party culture", they were threatened with academic consequences, the lawsuit claims.

Prof Heatherton has apologised for behaviour that he said could have been taken the wrong way. His lawyer, Julie Moore, said in a statement emailed to the BBC that incidents involving him have been "grossly mischaracterised".

Prof Heatherton "categorically denies playing any role in creating a toxic environment" and "is disturbed by the graphic allegations", according to his lawyer.

He says that he never socialised or had sexual relations with students, and also says he wasn't aware of the alleged behaviour of the other two nor would have he have condoned it.

Prof Whalen and Prof Kelley could not be immediately reached for comment.

Plaintiff Kristina Rapuano alleges Prof Kelley forced her to drink heavily with him while at a conference and raped her - and then began denying her academic guidance if she rebuffed his sexual advances.

Another plaintiff, Vassiki Chauhan, alleges similar behaviour from Prof Whalen, saying he pressured her into drinking with him and then forced himself on her.

The lawsuit also describes an unnamed student who reported Prof Heatherton for groping her, only to be told by the department chair to not "make a fuss". Prof Heatherton received a promotion shortly after.

What's the background?

In April 2017, a group of female graduate students reported the professors' behaviour to Dartmouth's Title IX office - an office meant to handle gender discrimination in accordance with US Department of Education rules.

But, the lawsuit alleges, the college then took steps to silence the 27 complainants, including expulsion, handing out unwarranted failing grades and publicly denouncing the victims.

It also claims Dartmouth took no action against the professors until last October, when the Title IX investigation was leaked to US media, resulting in the New Hampshire Attorney General opening a criminal investigation as well.

The college then hired outside counsel to independently investigate the matter, but that investigation was stopped this July, when Prof Heatherton and Prof Kelley retired and Prof Whalen resigned, according to the campus newspaper.

Justin Anderson, vice-president of communications at Dartmouth, told the BBC in an emailed statement that the school "respectfully, but strongly, disagree[s]" with the characterisation and "will respond through our own court filings".

The statement said the school "took unprecedented steps toward revoking [the professors'] tenure and terminating their employment".

Media playback is unsupported on your device Media caption How US teens talk about sexual assault

The three men were also banned from Dartmouth's campus and any school events.

"We remain open to a fair resolution of the students' claims through an alternative to the court process," Mr Anderson said.

In addition to the $70m in damages, the plaintiffs are requesting an order requiring the school to implement policies to fix the "hostile environment" and handle harassment claims swiftly.