Israeli survivors of the October 7 attacks and relatives of victims are stepping up efforts to get the International Criminal Court prosecutor to scrutinise Hamas' crimes as part of his investigation into the attack and Israel's response in Gaza.

"We want to make sure that the world acts and that their freedom is hindered," Udi Goren, cousin of 41-year-old Tal Haimi who was abducted on October 7, said of leaders of the Palestinian group Hamas. Haimi was later confirmed dead, his body still being held in Gaza.

Israeli survivors of the October 7 Hamas attack and families of victims want the court to target Hamas leaders with arrest warrants.

"We want to ... make sure that the leaders of Hamas are taken into custody or that they cannot leave Qatar anymore and that this puts pressure on them to release the hostages," Goren said, speaking at Israel's Ben Gurion airport.

Goren was among a group of around 100 family members of hostages preparing to fly to the ICC's headquarters in The Hague.

Israel is not a member of the ICC and does not recognise its jurisdiction.

But prosecutor Karim Khan reaffirmed to Reuters this week that the court has jurisdiction over the events of October 7 and they form part of the court's investigation. He declined to comment further on the ongoing investigation.

The Israeli hostages' families, who carried pictures of missing loved ones as they prepared to head to The Hague, will file the latest in several so-called article 15 communications on behalf of Israeli victims.

These legal filings are meant to provide information to the prosecution and are part of a wider push to get the ICC to act against Hamas leaders.

Testimonies

In a sign that the ICC's investigation is moving forward, lawyer Yael Vias Gvirsman, who represents another group of Israeli victims, told Reuters that a handful of her clients gave testimony directly to ICC investigators in The Hague last week.

"It was a significant next step for the investigation. Investigators sat down with victims for very long hours to hear personal accounts by key witnesses of several crime scenes of the October 7 attacks," said Vias Gvirsman, who represents 200 Israeli victims from 42 different families at the ICC.

On October 7, Hamas carried out a cross-border raid on southern Israel in which 1,200 Israelis were killed and around 240 were taken hostage, according to Israeli tallies.

It sparked the ongoing Israeli military offensive in Gaza which has laid waste to much of the densely-populated strip of land on the Mediterranean and left over 28,000 Palestinians dead, according to Gaza health officials.

The case at the ICC is separate from the genocide case launched against Israel at the International Court of Justice or World Court also based in The Hague.

The World Court is a United Nations court that deals with disputes between states while the ICC is a treaty-based criminal court focusing on individual criminal responsibility for war crimes, crimes against humanity and genocide.

The Palestinian territories were admitted as ICC members in 2015, which gives the court jurisdiction over atrocity crimes committed by anyone on that territory and by Palestinians on Israeli territory.