The Trump administration on Friday cut off tens of millions of dollars for health care programs and other aid in Yemen, rejecting pleas by humanitarian groups and some members of Congress to delay the decision as the coronavirus spreads across the Middle East.

American officials said the move was a necessary response to longstanding interference by Houthi rebels who control the northern part of Yemen. They have been fighting a civil war for the past five years and have imposed harsh restrictions on organizations trying to deliver aid. The fighting has killed thousands of civilians, and millions more face starvation in what the United Nations has labeled the world’s worst humanitarian crisis.

But as a pandemic looms, the American decision created major funding gaps for dozens of programs run by the United Nations and private aid groups, including efforts to supply the Yemenis with hand soap and medicine and to staff clinics with health care workers, humanitarian officials said.

Citing conditions that have already made Yemen a breeding ground for disease, the officials said they feared that populations weakened by hunger and packed into refugee camps would be further decimated by the coronavirus.