The US has been battling a deadly virus outbreak at its airports since early October, but it’s not known whether it has the resources or people to contain the spread of the disease.
The World Health Organization said on Thursday it had identified 513 new cases, up from 477 on Wednesday.
The number of confirmed cases in the United States rose to 4,093, according to a statement from the agency.
This is the first time the US has reported the total number of new cases.
US President Donald Trump is in Liberia to visit a church.
The White House said on Friday that Trump was “working with our allies to combat this virus outbreak”.
But the president’s administration has faced criticism over the pace of the response.
The US Centers for Disease Control and Prevention said it has seen an uptick in cases in some of the country’s most isolated counties.
The agency has sent a team of doctors and nurses to five counties, but only four have reached their targets.
At least 17 people have died of the Ebola virus, which has killed more than 8,400 people in the three years since it emerged in Guinea, Liberia and Sierra Leone.
“The outbreak of this disease is a global health crisis, and the response must be coordinated, effective, and robust,” CDC director Tom Frieden said in a statement.
Meanwhile, the WHO said on Wednesday that its efforts to combat the virus had been hampered by “overly optimistic” estimates.
WHO’s top infectious disease expert, Dr Tom Friedan, said he feared the “lack of information and knowledge about the epidemic”.
“The most likely scenario is that the current outbreak is going to go on for some time,” Friedan told the BBC.
Trump, who is visiting a US church, visited Liberia in December to meet with local officials and meet with the families of the dead.
But on Thursday, he said the US was not ready to commit to a plan to help combat the Ebola outbreak in West Africa.
He said he was also “very disappointed” that the country had “not taken the necessary steps” to control the virus.
He has promised a plan by January for a joint military task force to fight the virus in the region.