How the 'law of war' could apply to an Israeli ground invasion of Gaza

With Israel appearing to be on the cusp of a ground invasion into Gaza, President Joe Biden and other world leaders this week said the Jewish state has the right to defend itself against the recent brutal attacks by Hamas.

At the same time, they warned, Israel must abide by the "law of war" in protecting innocent Palestinians living in Gaza.

But with the prospect of hundreds, if not thousands more Palestinian civilians killed, can Israel do both? And could either Israel or Hamas be prosecuted for war crimes?

Here's what to know about international humanitarian laws and how they apply in the Israeli-Hamas conflict in Gaza.

What are the rules of war?

Most countries, including the U.S. and Israel, recognize a set of international humanitarian laws and resolutions embraced since World War II, including the Geneva Conventions. The agreed upon laws of armed conflict call on countries acting in self-defense to protect civilians from harm, provide aid to the wounded on the battlefield, and not to mistreat or humiliate prisoners of war.

The Geneva Conventions also specifically include rules against "collective penalties," including intimidation, terrorism, stealing and reprisals against civilians.

Hamas, which rules Gaza, violated these international laws on Oct. 7 when it launched a brutal surprise attack on Israeli civilians, experts say. The militant group, designated a terror group by the U.S. government and accused of violating international law in previous attacks, gunned down Israeli civilians in the street and killed others in their homes, including young children and babies. In all, more than 1,400 Israelis were killed and 4,500 people have been injured, according to Israeli authorities.

An estimated 200 other Israelis, including elderly women and toddlers, have been taken hostage by Hamas inside Gaza, Israel says.

Republican lawmakers in particular have defended Israel's right to self-defense, much as when the U.S. did launched an attack on Afghanistan after 9/11.

"Hamas’ actions were not just acts of 'terrorism' or 'terrorist attacks," said Rep. Michael McCaul, the Texas Republican who chairs the House Foreign Affairs Committee. "Rather, the assault was carried out by a genocidal organization and comprised nothing less than the full range of atrocity crimes under international law."

What about Israel?

Some foreign leaders and international groups including the United Nations have accused Israel of breaking international humanitarian laws in its retaliatory attack on Gaza.

They specifically cite Israel's decision to withhold food, water, electricity and fuel from Gaza for nearly two weeks as a form of "collective punishment" prohibited under the Geneva Conventions. They also cite the high death toll in Gaza being cited by Palestinian Health Ministry officials, including 5,000 deaths and 15,000 wounded.

In recent days, aid trucks carrying some supplies have trickled into Gaza, although aid workers say it's not nearly enough.

"It is collective punishment on a besieged and helpless people. It is a flagrant violation of international humanitarian law and a war crime," said Jordan's King Abdullah II, an ally of the West.

When asked to comment, the Israeli embassy in Washington responded that Israeli has "made clear that its defensive operations will be conducted in accordance with international law, including international humanitarian law even as it fights a terrorist group that has total disdain for the law and for human life - whether Israeli or Palestinian. Any suggestion to the contrary is without foundation."

Biden and other U.S. officials have stopped short of criticizing Israel, instead making the case that minimizing civilian deaths is in their long-term interest.

"The Israeli government’s decision to cut off food, water and electricity to a captive civilian population threatens not only to worsen a growing humanitarian crisis; it could further harden Palestinian attitudes for generations, erode global support for Israel, play into the hands of Israel’s enemies, and undermine long term efforts to achieve peace and stability in the region," said former President Barack Obama in a lengthy post on the online site Medium.

Why this gets so complicated

While most nation states -- including Israel -- have agreed to abide by international humanitarian laws, they don't necessarily agree on how those laws apply in Gaza or what should happen if they are violated.

For example, some dispute whether fighters for terrorist groups qualify for certain international protections. What constitutes a valid military target is another question, especially since Hamas is accused of using civilians as "human shields."

"If Hamas holes up in a building -- whether it's a hospital or mosque -- it becomes a valid military target," said Mick Mulroy, a former deputy assistant secretary of defense for the Middle East and an ABC contributor. "That said, every reasonable step should be taken to eliminate or reduce civilian casualties (and) has to be done."

Countries also don't agree on how war crimes should be prosecuted, with the U.S. and Israel among several countries that don't recognize the International Criminal Court.

Complicating matters is Gaza itself. With 2 million residents packed into a strip of land only about 25 miles long and 7.5 miles at its widest, Gaza is considered among the most densely populated places on Earth with Hamas operating alongside civilians.

Biden's top military aides say any effort by Israel to clear Gaza of Hamas through a ground operation will be a grueling monthslong fight with significant casualties.

Defense Secretary Lloyd Austin, who led the U.S. effort to clear Islamic State fighters from Mosul, said a lesson learned from the Iraq war was "how to account for civilians in the battle space" and to ensure civilians have evacuation routes.

"They are a professional force," Austin told ABC's "This Week" this past Sunday of the Israeli forces.

"And we will continue to encourage them to make sure that they're doing things in accordance with the law of war," he added.