Five countries, including South Africa and Bangladesh, on Friday called for an International Criminal Court investigation into the Israel-Hamas war which has left thousands of dead, its chief prosecutor said.

Amid international concern over the growing toll, the demand was made as families of some of the Israelis taken hostage by Hamas in their October 7 attacks that unleashed the war also sought ICC action.

ICC chief prosecutor Karim Khan said South Africa, Bangladesh, Bolivia, Comoros and Djibouti — all ICC members — had sought an investigation of "the situation in the state of Palestine".

Khan said in a statement that an investigation into events in the Gaza Strip and the occupied West Bank started in March 2021 now "extends to the escalation of hostilities and violence since the attacks that took place on October, 2023."

Khan, who recently went to the main crossing point between Gaza and Egypt, said his team had collected a "significant volume " of evidence on "relevant incidents" in the war.

He appealed for more evidence to be submitted and added: "I will also continue my efforts to visit the state of Palestine and Israel in order to meet with survivors, hear from civil society organisations and engage with relevant national counterparts."

Israel is not an ICC member and Khan said: "I call upon all relevant actors to provide full cooperation with my office."

Israel says that 239 people from several countries were seized by the Palestinian militant group when its fighters staged the October 7 attacks in which some 1,200 people, mainly civilians, died.

The hostage plight has become a major issue in Israel as it has pursued an air and ground campaign which the Hamas-run health ministry in Gaza says has left 12,000 dead.

Just as lawyers for the families of some of the Gaza Palestinian dead have sought ICC action, families for the hostages demanded that Khan issue warrants for Hamas leaders.

"The inquiry is advancing," Francois Zimeray, a lawyer for nine of the families, told AFP after the meeting.

He said he submitted a dossier on behalf of some of the families who want warrants issued for war crimes and genocide.

Any person or group can make a request to the ICC but it is not obliged to take up a case.

Legal experts have told AFP that Hamas and Israel could face war crimes charges over the conflict.

The ICC inquiry started in 2021 was into alleged war crimes by Israeli forces, Hamas and other Palestinian armed groups.

Even though Israel is not an ICC state party, Zimeray said: "We have Israelis who trust the court, the sincerity of the prosecutor and the professionalism of his team.

"That contributes to showing them that the court is capable of bringing justice for the crimes they have suffered, that their family has suffered."