Nicholas D. Kristof(CREDIT: Damon Winter/The New York Times)

IN THE NUBA MOUNTAINS, Sudan — It’s not clear whether the Sudanese air force was trying to bomb the village of grass huts or the girls high school next to it.

Hamida Osman, 23, simply knew that a Sukhoi fighter jet was roaring toward her village. She grabbed her only child, Safarina, 2, and jumped into the foxhole that the family had built for those frequent occasions when Sudan decides to bomb its people.

Inside the foxhole, Hamida used her own body to try to shield her daughter. They heard the sound of bombs whistling downward, and then there were two enormous explosions.

The next thing Hamida knew, she was covered with blood and had shrapnel wounds to her arms and legs. She looked down. A piece of shrapnel had taken away much of Safarina’s head.

Another day, another dead civilian. President Omar Hassan al-Bashir of Sudan, having committed crimes against humanity in South Sudan and Darfur, is now waging them with equal impunity in the Nuba Mountains in the far south of the country, and major nations are once more reacting mostly with indifference. With President Barack Obama headed to East Africa shortly, let’s hope he raises these atrocities and pushes for humanitarian access to the Nuba Mountains.

Limping from her injuries, Hamida showed me where the bombs had struck beside her now-incinerated hut.

“I don’t know what they’re trying to hit,” she said, “but they’re always dropping bombs on homes here.”

Sudan is deliberately bombing civilians and girls schools as part of its brutal counterinsurgency campaign against tens of thousands of armed rebels in the Nuba Mountains. The aim seems to be to terrorize the population and depopulate the area.

To keep out aid and eyewitnesses, Sudan bars visits by aid workers, diplomats and journalists. I slipped in through rebel lines without a visa, as I did on my three previous visits to the Nuba Mountains.

The village of Endeh rebuilt a school near caves used as shelter during bombings. When some schoolchildren showed me the caves, I noticed a freshly shed snake skin, from a spitting cobra. The villagers gently explained to me that cobras are, on balance, less terrifying than bombs.

The bombs have fallen in Nuba for four years and they accelerated early this year. Nuba Reports, a monitoring organization, counted 1,764 bombs dropped between December and February, more than ever before in a three-month period.

This isn’t exactly the same as Sudan’s slaughter in Darfur, for that has involved militias burning villages. Here in the Nuba Mountains, the rebels keep out militias, so Sudan kills from the air with bombs, artillery shells and cluster munitions. Bashir also blockades the area to keep out all food, medicine and supplies. Sudan even bombs trucks carrying food, and its denial of food and medicine probably kills more civilians than the bombings do directly.

The blockade of medicine is particularly infuriating. Only 5 to 10 percent of children in rebel-held areas get vaccinated, and one of the biggest measles outbreaks in Africa last year occurred in the Nuba Mountains.

UNICEF and Gavi, the Vaccine Alliance, are reluctant to send in vaccines for fear of antagonizing the Sudanese government and losing access in other parts of Sudan. So parents see their children dying not only from shelling but also from measles.

Let’s demand humanitarian access — and if it is not granted, aid agencies should send in medicine anyway. It’s unconscionable to let children die because of diplomatic protocol.

There are precedents. In the late 1980s, Sudan similarly blocked aid to rebel-held areas in the south, and the Reagan and first Bush administrations worked with UNICEF to start Operation Lifeline Sudan, sending in aid directly to needy areas. Today we need a new Operation Lifeline.

To his credit, Obama has quietly provided food to the Nuba Mountains, thus averting starvation. It’s a model of what could also be done with medicine. But Obama overall has been weaker than the four previous presidents in standing up to Sudan.

As for Safarina’s killing, it’s unclear whether Sudan was aiming for her village or the girls school. It speaks volumes that Sudan regularly targets both villagers and schoolgirls.

It’s a brutal way to live, and in the case of children like Safarina, to die. And as long as world leaders and aid agencies acquiesce and Sudan pays no price for its savagery, nothing will change.

— Nicholas Kristof is a columnist for The New York Times.