The International Criminal Court chief prosecutor, Karim Khan, has vowed to intensify efforts to investigate alleged war crimes in Gaza following his visit to Israel and the Palestinian Territories.

Khan stressed his visit was "not investigative in nature" but said he was able to speak to victims on both sides of the conflict.

More than 15,200 people have been killed in the besieged territory of Gaza, according to the Palestinian resistance group Hamas, in more than eight weeks of combat and heavy bombardment.

"My office will further intensify its efforts to advance its investigations in relation to this situation," Khan said.

"Credible allegations of crimes during the current conflict should be the subject of timely, independent examination and investigation."

Opening its doors in 2002, the ICC is the world's only independent court set up to probe the gravest offenses including genocide, war crimes and crimes against humanity.

It opened an investigation in 2021 into Israel as well as Hamas and other armed Palestinian groups for possible war crimes in the Palestinian territories.

Khan has previously said this investigation now "extends to the escalation of hostilities and violence since the attacks that took place on Oct. 7, 2023."

However, ICC teams have not been able to enter Gaza or investigate in Israel, which is not an ICC member.

The war broke out following a Hamas incursion into Israel, which then retaliated with indiscriminate attacks on Gaza.

Khan said he witnessed "calculated cruelty" at the sites attacked by Hamas.

He also emphasized that "the manner in which Israel responds to these attacks is subject to clear legal parameters that govern armed conflict."

Acknowledging that conflict in densely populated areas such as Gaza was "inherently complex," international humanitarian law must still apply, Khan said.

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

Five countries called in mid-November for an ICC investigation into the Israel-Hamas war, with Khan saying his team had collected a "significant volume" of evidence on "relevant incidents."

Khan also called for humanitarian aid to be allowed into Gaza and not be seized by Hamas.

"All actors must comply with international humanitarian law. If you do not do so, do not complain when my office is required to act," he warned.