Secretary of State Marco Rubio on Saturday announced the U.S. will revoke visas held by South Sudanese passport holders and no others will be issued, effective immediately.

Rubio attributed the change to "the failure of South Sudan's transitional government to accept the return of its repatriated citizens in a timely manner," according to a statement posted on X.

U.S. officials and travelers inside the African nation of Sudan are being encouraged to shelter in place as gunfire and explosions rocked the capital of Khartoum.

The paramilitary Rapid Support Forces (RSF) are clashing with Sudan's army, and the RSF claimed Saturday it had seized the presidential palace and taken control of the city's airport.

Pope Francis on Friday became the first pope to visit South Sudan — fulfilling a yearslong hope to carry out an ecumenical trip to the war-torn country.

The pope has called his Feb. 3-5 visit to Juba, South Sudan’s capital, a “pilgrimage of peace.” His Anglican counterpart, Archbishop of Canterbury Justin Welby, along with the moderator of the Church of Scotland, Iain Greenshields, will visit the newest African nation together.

Pope Francis had spoken about the possibility of the trip as early as 2017, fewer than four years after the outbreak of civil war in 2013.

A young Ukrainian mother and 41-year-old man from South Sudan had similar stories to tell on a recent morning in the northern French city of Calais. Both described fleeing war: Yuliia Vyshnivecka had escaped the Russian invasion with her 4-year-old daughter; Ahmed had left amid a civil war. Both were hungry, exhausted and faced the possibility of never reaching their desired destination: Britain.

“If I don’t get the visa, I’ll go back to Ukraine,” Vyshnivecka said, close to tears.

In the weeks leading up to South Sudan’s independence in July 2011, two sounds were inescapable in Malakal's market. Loudspeakers alternated between blasting the country's newly composed national anthem and President Obama’s “Yes We Can” speech. For many South Sudanese, the speech, with its references to slaves and abolitionists, resonated at a visceral level.

Now, nineteen months into a new civil war, as President Obama lands in neighboring Kenya, that marketplace and the dream of a peaceful future for the world’s newest country lies in ruin.

Three crew died, while one survived, said the UN mission in South Sudan, adding that an inquiry was under way.

A UN official told the AP news agency the Mi-8 helicopter had apparently been shot down.

Thousands of people have been killed this year in bitter fighting between South Sudan's army and rebel forces.

Bentiu, capital of the oil-rich Unity state, has changed hands several times but a ceasefire agreement is currently in place.