(Refiles Sept. 2 story to remove last name of community spokesman.)

FILE PHOTO - South Sudan's President Salva Kiir attends the launching of the National Dialogue committee in Juba, South Sudan May 22, 2017. REUTERS/Jok Solomun

WAU, South Sudan (Reuters) - After four years of civil war marked by brutal attacks on civilians, the United States is reviewing its support for South Sudan, USAID administrator Mark Green told the country’s President Salva Kiir in talks in the capital Juba.

Green, on his first trip to Africa as U.S. President Donald Trump’s new aid chief, said he urged Kiir to take a new round of regional peace talks seriously and called for an immediate ceasefire.

He met with Kiir for 45 minutes on Friday to deliver a blunt message from Washington amid concerns over atrocities, growing instability, lawlessness and the treatment of aid agencies.

The meeting signaled that the Trump administration was reconsidering backing for Kiir, who came to power with the support of Washington when oil-rich South Sudan won independence from neighboring Sudan in 2011 following decades of conflict.

But the world’s youngest country dissolved into civil war in 2013 after Kiir, an ethnic Dinka, fired his deputy Riek Machar, a Nuer. The conflict has been punctuated by gruesome massacres of civilians and widespread rape. Ethnic militias have divided the country into a patchwork of fiefdoms.

Nearly four million people – around one-third of the population – have fled their homes, creating the continent’s biggest refugee crisis since the 1994 Rwandan genocide. Last year, fighting spread to the southern Equatoria region, the country’s breadbasket, briefly plunging parts of the country into famine in early 2017.

“While it is true that we support the people of South Sudan, it is just as true that the situation has deteriorated to the point where a serious re-examination of U.S. policy is appropriate,” Green said in an interview embargoed until he had left the country because of security concerns.

“I told him that in the next few weeks we are undertaking a complete review of our policy toward South Sudan,” said Green, who emphasized that his discussions with Kiir were “cleared at the highest levels” in Washington.

The U.S. is the biggest donor to the massive U.N.-led humanitarian effort in South Sudan. It spent about $518 million in 2017, and has spent $2.7 billion since 2013.

Green said he listed U.S. concerns over humanitarian access and treatment of aid organizations. More than 80 aid workers have been killed since the conflict began and aid organizations have complained their movements are often restricted by the government.

Kiir disagreed with the U.S. assessment of the situation. He denied that government forces were behind the violence and said a unilateral ceasefire had been in place since May.

“He disagreed with our assessment that there are problems with humanitarian access,” said Green, a former Republican congressman from Wisconsin and ambassador to Tanzania. “I wanted him to understand that we’re serious about a review.”

Rights groups have long pressed the United States to crack down on South Sudan’s leaders and to impose sanctions that target individuals behind the violence.

A U.S. attempt to get a U.N. weapons embargo late last year failed. China, the biggest investor in South Sudan’s damaged oil fields, said it felt the embargo would not help.

The violence has slashed oil production and fueled hyperinflation, leaving the government with little money to pay its army, which has been blamed for increased looting of warehouses that store food aid.

FLEEING INSECURITY

Green traveled on Saturday under heavy guard to a U.N.-run camp for 32,400 people in Wau, a two-hour flight from Juba.

There are an estimated 220,000 civilians in six U.N.-run sites around the country. The one in Wau has been under U.N. protection since June 2016. Almost all the people who live in the camp have homes in Wau that they are too afraid to live in.

James Angamy, a teacher from Wau, is among the newest arrivals. He said he fled after soldiers and men in plain clothes went door-to-door in his Nazareth neighborhood accusing some residents of supporting rebels.

He was among a group of 12,000 people that arrived at the camp in April this year.

Angamy wants peace but he does not believe the government wants to end the war.

“The United States must convince him (President Kiir) to stop the fighting,” said Angamy, a community leader in the camp.

U.N. workers say civilians in the camps leave the site during the day but return at night, when most of the attacks on civilians occur.

“I believe there are tremendous problems of insecurity,” Green said, reflecting afterwards on what he saw in Wau. “It certainly doesn’t square with what we heard” from President Kiir, he said.

Green repeated that Kiir needed to take urgent action to end the insecurity by implementing a ceasefire.

“The president believes it’s safe and that there is security and that humanitarian workers aren’t at risk. What we saw in Wau is completely in contrast to that,” said Green.