U.S. Ambassador to the United Nations Nikki Haley meets South Sudanese refugee children at the Nguenyyiel refugee camp in the Gambella region in Ethiopia on Oct. 24, 2017. (Tiksa Negeri/Reuters)

U.N. Ambassador Nikki Haley warned South Sudan's president Wednesday that U.S. aid and other assistance were at stake, as Washington seeks to boost pressure on a leader it blames for helping plunge the world's youngest nation into civil war.

"The United States is at a crossroads," Haley said she told President Salva Kiir, a day after she heard refugees' horrific stories of violence and cruelty they claim were carried out by Kiir's forces in a conflict largely fought along tribal lines.

"We have to decide how we're going to look at South Sudan going forward, and that will be based on how he goes from here," she said. "And based on his actions the United States will act accordingly."

In the balance is billions in U.S. aid, a potential international arms embargo and the goodwill of the United States, which gave critical backing to South Sudan's independence from Sudan in 2011.

The United States has distanced itself from Kiir, the cowboy hat-wearing former rebel leader who presided over the promising birth of a nation blessed with oil and other natural resources.

But it fell to Haley to deliver an ultimatum.

"It was a very honest conversation. I basically said the United States had invested well over $11 billion in South Sudan and into him, and that we were now questioning that investment. I told them that he couldn't deny the stories about his military," which include allegations of rape, murder, kidnapping, forced labor and the use of child soldiers.

Haley claimed Kiir did not deny those allegations. There was no immediate word from Kiir or South Sudanese officials about the meeting.

[The dilemma posed by South Sudan]

"To his credit, he acknowledged everything I was saying," Haley said. "He listened to everything I was saying and he was not defensive."

Haley spoke to reporters traveling with her immediately after two lengthy meetings with Kiir, one of them a longer-than-expected private session. U.S. expectations include an end to violence snd full and consistent access for humanitarian groups, she said.

"I told him that we need to see him right the ship," she said.

On Tuesday, Haley toured a sprawling refugee camp in Ethiopia's Gambella region.

She ducked into a makeshift home for a newly arrived family of five, and heard the harrowing story of a weeks-long walk to flee renewed fighting across the border in South Sudan.

Haley crouched in the mud beside a nursing mother inside a hut that was little more than a tarp stamped with a U.N. humanitarian agency logo stretched over a frame of sticks. She promised to convey more details to U.N. colleagues and the Trump administration about the plight of the more than 400,000 South Sudanese now housed in Ethiopia. The U.N. estimates that 35,000 have arrived just since the end of September.

"I was mad when I left the camp. How do you not go through listening to those women talk and hearing what their families went through and not just be totally angry at those that are responsible?" Haley said afterward.

Inside a stifling, low-slung building reserved as a "women- and girl-friendly space," one woman broke down in sobs as she and two others told Haley stories of rape, murder and survival.

One woman told Haley that her family was killed — she did not say by whom but suggested that it was South Sudanese Army forces — and her baby thrown into a fire. Then, the woman claimed, she had been forced to eat the flesh.

[South Sudan is a disaster. Its president says: Not my fault.]

"We want to go home," one woman said, according to a U.N. translator. "We need our leader in the country."

That was a reference to former vice president Riek Machar, now in South Africa. Although some South Sudanese see Machar as their protector, the United States has long viewed him as part of the problem and has not advocated his return.

One woman told Haley that she blamed former president Barack Obama for the spiral of violence that began in 2013, and for the failed reconciliation effort in 2015. Haley looked startled at that, but did not respond.

Names of the women who spoke to Haley were not provided by the U.N. or humanitarian groups that serve the camp to protect their privacy and safety. Reporters were allowed to listen from several feet away.

Haley did not say that she would advocate for more U.S. humanitarian aid.

The Obama administration attempted to foster reconciliation talks between Kiir and Machar, and blamed both for squandering the democracy they helped to found.

"President Obama didn't do this to these women," Haley said in a second interview. "I think their perception is that they were let down by the United States back in 2013 when they really needed us."

Haley also toured a U.N.-run camp in Juba for internally displaced people. As Haley met with a family, protesters from Machar's Nuer tribe gathered outside, shouting "down, down, Salva Kiir." Kiir is a member of the rival Dinka tribe.

One held a sign reading, "Salva Kiir is a killer and must go!"

Haley and her party were quickly hustled into waiting cars.

Her five-day visit to Africa this week is heavily focused on South Sudan.