(CNN) -- The Ebola outbreak is much worse than official figures show and is "spiraling out of control," a leading U.S. official said Tuesday -- due in part, he said, to some countries that inadvertently have made it harder to corral the deadly disease.
Centers for Disease Control and Prevention Director Dr. Tom Frieden offered his stark commentary to CNN a day after Ellen Johnson Sirleaf, the president of Liberia, voiced dissatisfaction with the world response so far.
"In a way, we feel saddened by the response," President Sirleaf said.
More than 3,000 people have been infected by Ebola in Liberia, Guinea, Sierra Leone and Nigeria since the first documented cases in December, according to the World Health Organization. At least 1,552 have died.
Making it worse, Frieden said, is how other countries have turned their backs on those coming from countries where the outbreak is strongest, even if they don't realize it.
Measures to restrict flights and border crossings into the countries facing the outbreak were designed to contain the spread, but are having a paradoxical effect, he explained.
"This is making it really hard to get help in and to respond effectively to the outbreak," he said on CNN's "New Day."
"What we're seeing is a ... hugely fast increase in cases that's harder and harder to manage," he said. "The more we can get in there and tamp that down, the fewer cases we'll have in the weeks and months to come."
The president of Doctors Without Borders sharply criticized what she called the "global coalition of inaction" for focusing on insulating their nations instead of helping those in Africa who need it most.
Dr. Joanne Liu said centers run by her group have turned away sick because they are too full, as an ever-increasing number of people develop symptoms of Ebola.
"States with the required capacity have a political and humanitarian responsibility to come forward and offer a desperately needed, concrete response to the disaster unfolding in front of the world's eyes ... rather than limit their response to the potential arrival of an infected patient in their countries," Liu said.
In her CNN interview, President Sirleaf of Liberia appealed for other nations to "please work as partners with us" by offering monetary, health care, logistical and other assistance, yes, but also by giving moral and personal support to a problem that's affected millions already.
"Give us hope by joining us in this fight," Sirleaf said. "Don't instill fear. We need that hope, we need that assistance, we need for Liberians to know that this war can be won."
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