The U.S. has halted all U.S.-bound flights of Afghan evacuees from two main bases overseas after discovering a limited measles outbreak among Afghans arriving in the United States, a hitch that American officials warned will have a severe impact on an often-troubled U.S.-run evacuation.

U.S. Customs and Border Protection made the decision on the recommendation of the Centers for Disease Control and Prevention to halt the flights from U.S. bases in Germany and Qatar, according to a U.S. government document seen Friday by The Associated Press. The document cited unspecified “health safety concerns."

White House press secretary Jen Psaki said the temporary halt stemmed from discovery of measles among four arrivals in the United States.

The government document viewed by the AP said the halt would “severely impact” operations at Ramstein Air Base in Germany and have an “adverse effect” on the nearly 10,000 evacuees, many of whom it said have been there more than 10 days and are increasingly fatigued.

It was the latest problem in the Biden administration's rushed, chaotic and often violence-plagued evacuation of tens of thousands of Afghans and Americans and other foreigners from Afghanistan, which peaked with a more than two-week military airlift out of the Kabul airport. That shut down Aug. 30, when American troops withdrew. Thousands of Afghan evacuees remain in third-country transit sites, before being moved to the United States or other countries.

The halting of the flights is a problem for the United States in part because many of the evacuees already have been at the Ramstein base longer than the 10-day limit Germany set in allowing the U.S. to use the country as a transit site.

Germany and Qatar, along with Spain, Kosovo, Kuwait and other countries, agreed to temporarily host U.S. processing sites for evacuees after Kabul fell, after allies initially balked over worries of getting stuck with U.S. security problems.

Processing at many of the transit sites largely appears to be taking place in a peaceful and orderly fashion. That follows a suicide bombing and other attacks and violent incidents during the U.S.-run evacuation in Kabul, which killed more than 180 Afghans and 13 U.S. service members.

National Security Council spokeswoman Emily Horne said Friday that 32 Americans and U.S. green-card holders had left Afghanistan on Friday, 19 on a Qatar Airways flight and 13 others by land. It was only the second such evacuation flight allowed by the Taliban since U.S. troops left.

The U.S. government believes about 100 American citizens remain in Afghanistan, a State Department spokeswoman, Jalina Porter, said.

It was the same number the U.S. had given before the latest evacuation flights took out Americans. Porter said she could not immediately explain why the number had not changed.