AMNA NAWAZ: President Biden and the leaders of half-a-dozen European countries released a letter overnight endorsing Israel's right to defend itself, but also -- quote -- "calling for Israel to adhere to international humanitarian law, including the protection of civilians."

Nick Schifrin looks at those laws of war and whether they're being followed.

NICK SCHIFRIN: The rules that define armed conflict are a set of internationally recognized laws and resolutions that govern military targeting and require militaries to balance their priorities with protecting and warning civilians.

What we have seen on the ground so far, Hamas terrorists turned Israeli kibbutzim into ashes and a music festival into a massacre, more than 1,400 Israelis killed, hundreds taken hostage.

In Gaza, health authorities say more than 5,000 Palestinians are dead, nearly half of the population displaced, and some Gaza City neighborhoods reduced to moonscapes by Israeli airstrikes.

For more on the question of international law, we get two views, Pnina Sharvit Baruch, former legal adviser to the Israel Defense Forces and senior research fellow at the Israel Institute for National Security Studies, and Sari Bashi, human rights lawyer and program director at Human Rights Watch.

Thank you very much to both of you.

Welcome to the "NewsHour."

Pnina Sharvit Baruch, let me start with you.

Is Israel following the law of armed conflict?

PNINA SHARVIT BARUCH, Institute for National Security Studies: I was a legal adviser in the IDF, in the military, and the laws of armed conflict are entrenched in our commands, in the training.

We have legal advisers there.

We are -- it is important for us to be -- to abide by the rules, to be a law-abiding state.

But, of course, the application and the implementation relies on the circumstances.

This is -- there is a flexibility in the laws of armed conflict.

NICK SCHIFRIN: Sari Bashi, what do you see in the circumstances?

Do you believe Israel is abiding by the law of armed conflict?

SARI BASHI, Human Rights Watch: No.

So, this current escalation began on October 7, when Hamas-led fighters committed unspeakable war crimes against Israeli civilians, killing, massacring, and taking hostage, including children.

And the Israeli response, unfortunately, has been to target civilians in Gaza.

One of the first things the Israeli military did was cut off all supplies to Gaza, food, fuel, water, and electricity, which has set into motion a spiraling humanitarian crisis.

Punishing civilians in Gaza for the actions of fighters is collective punishment.

And it's a war crime under international law.

NICK SCHIFRIN: Pnina Sharvit Baruch, let's start with that topic.

The Israeli military very specifically cut off water, electricity that Israel provides to Gaza.

Is that collective punishment?

PNINA SHARVIT BARUCH: No, it's not collective punishment.

What the Hamas terrorists did was a brutal attack against the state of Israel.

They are clearly an enemy that is after us, that is there to -- main aim is to destroy the state of Israel.

Israel is acting fully in its right to defend -- its obligation, even, to defend its civilians.

The only thing that the law demands with regard to the civilian population of the enemy -- I'm talking here about supplying -- is that there will be no starvation and to allow the supply of basic humanitarian needs.

And Israel is doing that.

There have been trucks, I don't know how many, but many trucks going in the last few days through Rafah, to the civilian population.

So there is no starvation, is allowing that.

But to talk about a collective punishment, when we are really defending ourselves against this vicious enemy that is there -- and it's not just revenge.

It's not revenge.

Revenge is not the policy.

NICK SCHIFRIN: Sari Bashi, what about that argument?

The Israelis, the Egyptians, the Americans have figured out to get about three dozen or so trucks at this point through Rafah, and Israel is not obligated to continue sending in electricity and other items that it argues could be dual use for Hamas.

SARI BASHI: So, water is not a dual-use item.

Water is something that civilians need to drink.

And the Israeli army in an update yesterday to diplomats acknowledged that there are water shortages in Northern Gaza.

But their response was, well, those people should evacuate.

That's not what international law says.

Civilians need to be protected all the time.

What the Israeli authorities have done is deliberately cut the water and electricity that simply flows into Gaza.

They're also blocking fuel from entering the Rafah Crossing, the Southern Egyptian crossing.

The fuel is needed to deliver the very small quantities of aid that have come in.

The fuel is needed for hospital generators.

This is lifesaving equipment.

And deliberately impeding that passage is a war crime.

There's a very simple and very clear thing that needs to happen.

The Israeli government needs to immediately turn back on the electricity and water, stop blocking fuel from entering via Rafah, and take the steps necessary, as it has done in previous conflicts, to open its own crossing, so that the full panoply of humanitarian aid can enter for civilians in Gaza.

NICK SCHIFRIN: Pnina Sharvit Baruch, let me switch over to the Israeli air campaign that we have seen so far.

Some neighborhoods in Gaza City have been reduced, frankly, to moonscapes.

Law of armed conflict talks about proportionality.

Do you believe that the Israeli air force and the campaign so far has been proportional to the threat that Hamas poses and those Hamas targets that Israel says it's pursuing?

PNINA SHARVIT BARUCH: We have to understand that all the military infrastructure of the Hamas and the other terrorist organizations is within, is inside civilian buildings and under civilian buildings.

And, according to the law, when a civilian object is used for military purposes, it becomes a lawful military target.

Then, even when you do attack them, you have to examine, what is the military advantage and whether the collateral damage to harm to civilians expected would be excessive in comparison to the military advantage?

Israel is facing from the Hamas an existential threat.

We have 200,000 Israelis, internally displaced Israelis, villages that are burnt.

We cannot go back and live there.

The other enemies, Hezbollah and the Iran and other proxies, are looking to see.

If Israel is weak, they will enter the fight.

This could be the end of the state of Israel.

Yes, civilians, unfortunately, are harmed, but that doesn't mean this harm is excessive because of this huge military advantage that we have on the other side.

NICK SCHIFRIN: Sari Bashi, take on that point.

I personally have reported from Gaza inside wars in 2014.

And I have seen how Hamas uses mosques, schools, et cetera, as military bases.

SARI BASHI: So I would agree that the proportionality inquiry is case-by-case and specific.

My concern is that the Israeli military is dropping explosive weapons with wide-area effects in densely populated areas in ways that are predicted to kill civilians, and they're killing civilians.

And since this war began, the Israeli military has killed, on average, every day more than 100 children in Gaza.

That is not only what I would call excessive, to use Pnina's words.

It also violates a widely accepted new standard, including a standard that the United States has signed onto, about the need to avoid the use of explosive weapons with wide-area effects in populated areas.

If you continue to do that, you raise the risk of indiscriminate attacks, which are unlawful.

NICK SCHIFRIN: Pnina Sharvit Baruch, let's look into the future.

The United States right now is giving tactical and operational discussions with Israelis about how to conduct their ground invasion expected to start at any minute.

Will the IDF try its best to limit civilian casualties by using some of the smaller weapons and different techniques on the ground, or will it use overwhelming force?

PNINA SHARVIT BARUCH: It is in our interest to minimize harm to civilians.

It's also our legal obligation to take precautions, feasible precautions.

Of course, we will do whatever we can.

But, again, we have to understand Hamas has these tunnels under all the buildings.

They booby-trap buildings, civilian buildings, so that, if we attack a target, a tunnel in one place, it will lead to another house collapsing somewhere else.

It's a means -- they're using the Palestinian life as a means of warfare, of lawfare, of fighting us in the international arena.

So, what are we supposed to do, do nothing, allow them to come again and butcher us again, allow our other enemies to join when they think that we are weak?

And what are the options?

NICK SCHIFRIN: Sari Bashi, what is your message to the IDF as it launches its ground invasion, given the realities of how Hamas is embedded into Gaza City especially?

SARI BASHI: So the option and the requirement is to obey the law.

And the law has very specific protections for civilians.

I'm particularly worried about the many civilians who've remained in Northern Gaza.

The Israeli military asked or warned people in Gaza, one million people, to leave.

For many, that's impossible.

And the Israeli military last night dropped fliers warning people in Northern Gaza that, if they stay behind, they risk being considered to be part of -- to be complicit in terrorism.

That is a very, very dark sign of how they intend to treat civilians in Gaza.

NICK SCHIFRIN: Pnina Sharvit Baruch, Sari Bashi, thank you very much to you both.

SARI BASHI: Thank you.

PNINA SHARVIT BARUCH: Thank you.