WASHINGTON — Nations reeling from conflict, poverty and deficient health care will be unable to contain the coronavirus without significant international assistance, risking that the disease will ricochet back to recovering populations in a deadly global cycle, the United Nations warned in a new $2 billion appeal to combat the pandemic.

Even as they called on the world to fund defenses against the virus, U.N. officials also urged continuing donations to humanitarian crises to prevent those nations from becoming even more vulnerable to the disease.

“Countries battle their own catastrophes at home” and “are rightly prioritizing their citizens,” Mark Lowcock, the U.N. under secretary general for humanitarian affairs and emergency relief, said in an interview on Tuesday. “But the hard truth is, in order to protect their own people, it’s going to be smart to help the poorest countries engage for this response, too.”

The money to confront the coronavirus in 53 nations suffering from instability — in South America, Africa the Middle East and Asia — is not immediately available. Funds will be raised over the next nine months as U.N. agencies and private aid organizations combine efforts for the appeal, and for a new response plan that will be released Wednesday during an online news briefing. Details of the plan were provided in advance to The New York Times.