GEOFF BENNETT: It's the world's largest humanitarian crisis, yet aid groups say it has received far too little attention, even as Sudan's civil war enters its fourth year.

Sudan's conflict and the suffering it has created are growing more severe.

Nearly two out of every five people face emergency levels of hunger.

And humanitarian officials warn the crisis has been compounded by disruptions to global aid following the closure of the Strait of Hormuz.

As Nick Schifrin reports, the toll on civilians continues to mount.

A warning: Some images in this story are disturbing.

NICK SCHIFRIN: In the fields of Sudan, it's time for the harvest.

The colors may be bountiful, bright green and red, but the harvest is not.

Farmers are fighting three simultaneous battles, drought, displacement, and now a deficit of fertilizer and fuel.

The closure of the Strait of Hormuz has hiked prices for Sudan's farmers and reduced the country's access to food, just as parts of Sudan suffer from famine and the devastation of a brutal civil war that's entered its fourth year.

TJADA D'OYEN MCKENNA, CEO, Mercy Corps: People are suffering, and this is entirely manmade and can be stopped.

NICK SCHIFRIN: Tjada D'Oyen McKenna is the CEO of Mercy Corps, a humanitarian organization working on Sudan's front lines.

TJADA D'OYEN MCKENNA: Some people have had to resort to eating leaves to survive because of a lack of food.

And even when people do have access to it, the ability to afford it is even worse at this point.

We are seeing this irregularity of supply, as well as the price spikes are really locking in food insecurity and hunger situations for years to come.

NICK SCHIFRIN: What will happen to Sudan if the strait isn't open?

Cindy McCain was until recently the executive director of the World Food Program.

CINDY MCCAIN, Former Executive Director, World Food Program: In the worst-case scenario, the country could implode and just turn into complete anarchy.

NICK SCHIFRIN: The war has already pushed the country toward collapse, on one side, the government's Sudanese Armed Forces, on the other, the paramilitary rebel group, the Rapid Support Forces, or RSF.

Sudanese cities have become battlegrounds.

Both sides are accused of war crimes.

In Darfur, Sudan's largest region, where famine has been declared, the RSF is accused of genocide.

TJADA D'OYEN MCKENNA: What I'm seeing is a country and a population that is living with the effects going on into the fourth year of a war and crumbling civilian infrastructure that accompanies that.

MARCO RUBIO, U.S.

Secretary of State: Sudan remains a very frustrating situation.

NICK SCHIFRIN: Last week, Secretary of State Marco Rubio once again labeled Sudan a proxy fight.

Saudi Arabia and others support the Sudanese Armed Forces, and the United Arab Emirates support the RSF.

And foreign weapons and assistance have helped fuel the war.

MARCO RUBIO: The divisions between the UAE and Saudi Arabia have truly complicated our ability to bring that to an end.

What we're focused on there now is identifying two cities -- or four cities, two on each side, that will serve as points of distribution for humanitarian aid.

NICK SCHIFRIN: But humanitarians say the world has not put enough pressure or pressure or provided enough assistance to Sudan's neediest.

TJADA D'OYEN MCKENNA: It's shameful, really.

There are lives being lost that did not need to be lost because of this indifference that we're seeing.

In three years, going on four years into this conflict, we do not see any strong political will to end the conflict.

NICK SCHIFRIN: The humanitarian needs are staggering, tens of thousands dead, many buried in unmarked mass graves, like Mohamed Alswai.

More than a year ago, the RSF shot him dead and hastily buried him.

His brother Abubakar is only now able to provide him a proper re-burial.

ABUBAKAR ALSWAI, Brother Killed in War (through translator): It is so painful for us.

Even the kids have come to me and said: "Uncle Mohamed, Uncle Mohamed is dead.

Uncle Mohamed is buried outside."

NICK SCHIFRIN: And this is the world's largest humanitarian crisis; 30 million need assistance; 11 million are displaced.

Many have fled their homes into camps where there is not enough food or water.

The stories of sacrifice here are everywhere, Safiya Abu Bakr, whose husband was killed in a Sudanese airstrike, Hussein Sharif, shot in the head by an RSF sniper, giving him partial paralysis, and Fatima Mohammed, she and her kids separated from her husband by war.

FATIMA MOHAMMED, Displaced Mother (through translator): We are waiting for the war to end so we can return and live peacefully with our children and their father, and for the children to live securely.

This is all we hope for.

NICK SCHIFRIN: But theirs will be a hope deferred, because there is no end in sight to the hardships caused by the closure of the Strait of Hormuz or the war that has forced them to flee their homes.

For the "PBS News Hour," I'm Nick Schifrin.