Israel is at war with Hamas, the Palestinian militant group that is listed as a terrorist organisation by many Western nations, including the UK and the US.

The escalation follows an unprecedented attack by Hamas fighters, who claim to have fired over 5,000 rockets into Israel this weekend, as well as killing hundreds of Israeli civilians and troops, and taking dozens more hostage.

The Israeli government has compared the assault to 9/11 and Pearl Harbor, and the country’s ambassador to the UK told Channel 4 News that it represents the largest loss of Jewish life in a single day since the Holocaust.

Israel has responded with a massive military assault on the Gaza Strip, a Palestinian territory within Israel’s borders that has been controlled by Hamas since local elections in 2006. The Israeli ambassador to the UK told Channel 4 News that her government’s goal is “to make sure those atrocities will never be back again inside of Israel”.

The conflict is the largest in Israel’s 75-year history and is likely to claim more lives still.

The UN, the International Committee of the Red Cross (ICRC) and Human Rights Watch have warned both sides that they must not commit war crimes as hostilities escalate.

So, what is a war crime and what do we know about Hamas’s attack and Israel’s response?

This article contains details that some readers might find distressing.

Did Hamas commit war crimes in its attack on Israel?

Hamas’s surprise attack on Israel this weekend took multiple forms.

Thousands of rockets (Hamas puts the figure at 5,000; Israel says it’s likely to be much lower than this) were fired into Israeli cities including Tel Aviv, some of which killed and injured civilians. The Israeli death toll stands at 1,200 at time of writing.

Meanwhile Hamas gunmen broke through the border fence with Gaza, as well as using paragliders to enter Israeli territory, and began roaming through towns, shooting civilians and soldiers.

There is emerging evidence of the brutality of Hamas’s attacks. Some 260 bodies have been recovered from a festival that was taking place in the desert. Survivors describe gunmen descending on the party, shooting people and hunting down those who tried to hide in nearby woodland. Meanwhile hundreds of people, including children, have been killed in kibbutzim (small communities) near the border with Gaza.

Responding to the latest escalation of violence in Israel and Gaza, the ICRC said: “Killing civilians and ill-treatment are prohibited by the Geneva Conventions”.

The ICRC is an independent body that aims to uphold international law during war and violence. It represents both the Red Cross and Red Crescent humanitarian groups.

So-called “grave breaches” of the Geneva Conventions are considered war crimes. A grave breach includes “wilful killing”, which is why some experts are already saying that Hamas’s attacks on civilians this weekend could constitute a war crime.

Challenged by Channel 4 News’ Cathy Newman that Hamas’s attacks on Israeli citizens were unprovoked, a spokesperson for the militant group said on Saturday that “we were never thinking to attack civilians”.

Hamas fighters are also believed to have taken over 100 hostages from Israel. A spokesperson for the militants said dozens of captives are being held in “safe places” and in underground tunnels beneath Gaza.

Hamas said on Monday that every time Israel strikes “our people who are safe in their homes” without warning, it will execute a civilian hostage taken from Israel.

The ICRC made clear that hostage-taking is a breach of international law and a war crime.

There have also been allegations that Hamas fighters have raped or sexually assaulted women. The evidence for this is still emerging.

A reporter for US outlet Tablet quotes an eyewitness who told him “women have been raped” at the festival in the desert where 260 people are known to have died.

The Times of Israel newspaper reports seeing two videos that appear to show evidence of women having been sexually assaulted. The paper says that in one, a woman appears to be bleeding into her shorts, while another apparently shows a woman in her underwear lying on a truck.

Rape and sexual violence are illegal at any time, but they can also be war crimes if they are committed as part of an armed conflict.

Israel’s response to Hamas attack

On Monday 9 October, Israel’s defence minister Yoav Gallant announced his forces would impose a “complete siege on Gaza” in response to Hamas’s weekend assault. He said there would be “no electricity, no food, no water, no gas”. On the same day, the head of Israel’s infrastructure ministry ordered the cutting-off of Israeli water supplies to Gaza.

A siege is when forces control the ways in and out of a city, town or region to trap people inside. Siege tactics can constitute a war crime if forces are bombing civilian targets inside the city – or if they block food, water or essential supplies from the people there.

On Channel 4 News that evening, the Israeli ambassador to the UK, Tzipi Hotovely, said: “Gaza gets supplies from Egypt. Israel shouldn’t and mustn’t supply electricity to the Gaza Strip. This is not part of our obligations”.

Challenged by Channel 4 News’ Krishnan Guru-Murthy that the impact of the siege would be to starve civilians, Ms Hotovely said, “that’s your mistake.” She added: “It is Hamas to be blamed [for] anything that will happen to civilians.”

“We don’t have any obligation according to international law [to provide supplies to Gaza] because we are not occupiers in Gaza,” she said.

Responding to the latest crisis, the UN has warned that any siege that “endanger[s] the lives of civilians by depriving them of goods essential for their survival is prohibited under international humanitarian law”.

Meanwhile, Israel’s military has been striking targets across the territory. On Wednesday morning the Israel Defense Forces said they had hit more than 450 sites overnight. At least 950 Palestinians, including civilians, are believed to have died since Israel’s first retaliatory strikes this weekend.

In order to consider these war crimes, there would need to be proof that Benjamin Netanyahu’s forces had meant to target civilians. But even if it’s not deliberate, as we’ve previously reported, killing civilians can still break international law. Both sides have to make sure that any strikes are not indiscriminate.

The UN says that its Human Rights Office has gathered “information” that “indicates that Israeli air operations have also hit large residential towers in Gaza City and other residential buildings across Gaza, schools and premises of the UN relief and works agency, UNRWA, resulting in civilian casualties”.

The UN notes that “international humanitarian law is clear: the obligation to take constant care to spare the civilian population and civilian objects remains applicable throughout the attacks.”

However, a spokesperson for Israel’s military told Channel 4 News on 7 October that “we do not focus our attacks on people that are not involved, on civilians. We’ll be going after Hamas targets”. He said that “hopefully the collateral damage will be minimal”.

Human Rights Watch, an international nonprofit organisation based in the US, says that during previous violent clashes, “Israel has repeatedly carried out indiscriminate airstrikes that killed scores of civilians – wiping out entire families – and strikes that targeted civilians or civilian infrastructure, including destroying high-rise Gaza towers full of homes and businesses, with no evident military targets in the vicinity.”

The Israeli government has previously denied claims that it had carried out war crimes in Palestinian territories. In a statement in 2021, the prime minister’s office said: “Israel absolutely rejects the claim that it has carried out war crimes”.

The UN has urged parties to “spare civilian lives” in the latest conflict.