Boston, Massachusetts - President Joe Biden on Tuesday condemned what he said was sexual violence by Hamas during the October 7 attacks on Israel, claims that the Palestinian militants deny.

Biden also called for Hamas to release female hostages it is still holding in Gaza, claiming the group's refusal to free them had led to the breakdown of a truce with Israel.

"The world can’t just look away at what’s going on," Biden said at a campaign event in Boston.

"It’s on all of us – government, international organizations, civil society, and businesses – to forcefully condemn the sexual violence of Hamas terrorists without equivocation."

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Campaigners in Israel have derided what they see as a muted international response to gender-based violence during the attack.

Hamas in a statement Monday rejected accusations of rape and sexual violence as "unfounded lies."

Female Palestinian prisoners released as part of the week-long truce that expired on December 1 also reported being mistreated and threatened with sexual violence in Israeli jails.

Biden said there had been horrifying reports that Hamas "used rape to terrorize women and girls" during the attacks last month, in which Israel says 1,200 people were killed.

"Over the past few weeks, survivors and witnesses of the attacks have shared the horrific accounts of unimaginable cruelty" including rape, mutilation, and the desecration of bodies, he said.

"Hamas terrorists inflicting as much pain and suffering on women and girls as possible and then murdering them – It is appalling."

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Biden said that Hamas had "refused to let go" a number of women aged between 20 and 39 under a deal brokered by Qatar between Israel and the Palestinian group.

"These women and everyone still being held hostage by Hamas need to be returned to their families immediately. We’re not going to stop until we bring every one of them home and it’s going to be a long process," he said.

State Department spokesperson Matthew Miller said on Monday that Hamas likely held back on freeing female hostages because it did not want the women to speak publicly about sexual violence, but then admitted he had no concrete evidence for his claims.