Samantha Power said before arriving in Guinea that too many leaders were praising the efforts of countries like the United States and Britain to accelerate aid to the worst-affected nations, but were doing little themselves.
"The international response to Ebola needs to be taken to a wholly different scale than it is right now," Power told NBC News before boarding her plane.
She said many countries "are signing on to resolutions and praising the good work that the United States and the United Kingdom and others are doing, but they themselves haven't taken the responsibility yet to send docs, to send beds, to send the reasonable amount of money".
She will also visit Ghana, where the UN mission fighting Ebola is based, before meeting EU officials in Belgium.
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More than 10,000 people have contracted the Ebola virus, according to the latest World Health Organization figures.
Another west African country, Mali, was scrambling to prevent a wider outbreak after a two-year-old girl died from her infection following a 1,000-kilometre bus ride from Guinea. She was Mali's first recorded case of the disease.
An American nurse who was placed in quarantine after caring for Ebola sufferers in Sierra Leone has complained she was made to feel "like a criminal".
The new rules took effect in New York and New Jersey on Friday, the same day Hickox returned.
"This is not a situation I would wish on anyone, and I am scared for those who will follow me," Hickox wrote in The Dallas Morning News.
"I am scared about how health care workers will be treated at airports when they declare that they have been fighting Ebola in west Africa. I am scared that, like me, they will arrive and see a frenzy of disorganization, fear and, most frightening, quarantine."
She said there was a danger the new regulations could set back the fight against the virus.