What are the rules of war? And how do they apply to Israel's actions in Gaza?

Six days after a brutal attack by armed Hamas militants on Israeli civilians, Israel ordered an evacuation of more than 1 million Palestinians in northern Gaza ahead of what could be an unprecedented ground offensive there against Hamas.

"We are going to destroy Hamas infrastructures, Hamas headquarters, Hamas military," vowed Israeli Defense Minister Yoav Gallant as airstrikes were underway.

The U.S. and other nations have repeatedly warned Israel to follow the "rules of war."

But what are they? And will they prevent civilians from being hurt?

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

Is Israel bound by the rules of war?

Yes.

Israel has promised to abide by international humanitarian law including those under the Geneva Convention that seeks to minimize the impact on civilians, provide aid to the wounded on the battlefield, and not to mistreat prisoners of war.

In general, the U.S. military and Israeli Defense Force also rely on similar rules of engagement in military operations.

Israel insists it follows the rules of war and always has.

But there is disagreement by international groups about exactly what qualifies as a violation in a country's quest to defend itself against terror attacks, as well as whether Israel could be prosecuted through the International Criminal Court -- an entity Israel doesn't recognize.

Officials at the United Nations and European Union have accused Israel of already violating its promise not to harm civilians by cutting water and electricity to all of Gaza residents, including to hospitals. They also say it's impossible to ensure the safety of so many civilians by giving only 24 hours to evacuate to avoid the fighting.

Palestinian health authorities estimate 1,799 civilians have been killed in Israeli airstrikes, including 583 children, following Hamas' attacks that have killed at least 1,300 Israelis.

Ravina Shamdasani, spokesperson for the Office of the U.N. High Commissioner for Human rights, said Hamas' brutality doesn't "liberate" Israel from adhering to international humanitarian laws.

"It is absolutely crucial that Israeli leaders and global leaders make it unambiguously clear that international humanitarian law is an obligation. It is not optional, and that military operations must be conducted in full compliance with international law," she said.

President Joe Biden said he delivered that message directly to Israeli Prime Minister Benjamin Netanyahu this week, later telling reporters "that it is really important that Israel, with all the anger and frustration … they operate by the rules of war."

"And there are rules of war," Biden added.

How would the rules apply in this conflict? Would civilians be spared?

Avoiding harm to civilians though can fall into a gray area, particularly when it comes to a massive ground operation unfolding on a remarkably narrow strip of land. Gaza is among the most populated areas on Earth, roughly 7.5 miles at its widest and 25 miles long with some 2 million inhabitants.

Eric Oehlerich, a retired Navy SEAL and ABC News contributor, said that even with sophisticated weaponry, such an operation would be extraordinarily difficult to carry out with no civilians harmed.

"There isn't a force in the world that can deal with 40,000 (enemy) soldiers interspersed with civilians in that densely populated area" and have "zero" civilian deaths, said Oehlerich.

"It's impossible," he added.

One question will be what constitutes a valid military target, said Mick Mulroy, a former deputy assistant secretary of defense for the Middle East and retired CIA paramilitary operations officer.

Israel says that Hamas -- which doesn't abide by humanitarian laws in its deliberate attack on civilians last week -- uses Palestinian civilians and hospitals as shields.

"If Hamas holds up in a building -- whether it's a hospital or mosque -- it becomes a valid military target," said Mulroy, also an ABC contributor. "That said, every reasonable step should be taken to eliminate or reduce civilian casualties (and) has to be done."

What does all this mean for hostages held by Hamas and US citizens inside Gaza?

Oehlerich, who has participated in military operations to free hostages, said getting those hostages out using military force will also be extraordinarily tough. That's because Hamas will likely have gone to great lengths to hide the hostages, including possibly rigging secret tunnels or even the hostages themselves with explosives.

Oehlerich said success is more likely to come through backchannel negotiations with countries like Egypt and Qatar.

Israeli officials say its special operations forces have been operating inside Gaza in past days trying to locate hostages. The US is also working the Red Cross and the UN to establish "safe zones" for foreign nationals to leave, including Americans located within Palestine, according to a senior State Department official.

Beyond that, questions remain on how many innocent people will be hurt or killed inside Gaza. When asked by a reporter Friday what worries him most about the Israeli ground invasion, Biden had a one-word answer.

"Death," he said.

ABC News' Shannon Crawford, William Gretsky and Mary Bruce contributed to this report.