The Trump administration’s decision over the weekend to revoke visas for all South Sudanese passport holders adds to the mounting political and humanitarian challenges confronting the world’s youngest nation.

South Sudan faces the risk of civil war as tensions between its political leaders have escalated, especially since the authorities put the vice president under house arrest in late March. Millions of people are also facing hunger, displacement and disease outbreaks as violence intensifies and the United States cuts aid.

The sweeping visa ban, regional observers say, shows how Washington is retreating at a time of immense need for the East African nation, which it helped bring into existence nearly 15 years ago by supporting its bid for independence from Sudan.

“A massive storm is forming over South Sudan, and the visa ban only adds to the anxiety people have about all that could go wrong,” said Daniel Akech, the senior South Sudan analyst at the International Crisis Group, a nonprofit organization. “The timing and execution of it is just not right or helpful.”

On Saturday, Secretary of State Marco Rubio said he was revoking visas for South Sudanese nationals and preventing any more from entering the United States. The deputy secretary of state, Christopher Landau, said on social media that South Sudan had refused to accept the repatriation of one of its nationals.

The Trump administration has not said whether it would seek to deport South Sudanese nationals whose visas had been revoked. South Sudan’s government has not responded to the announcement of the visa ban, and a government spokesman did not respond to requests for comment.