Washington — The United States has pledged to provide $8 million to support the global response to the growing Ebola outbreak in Congo, officials said on Tuesday.

Health and Human Services Secretary Alex Azar announced a $7 million commitment on Tuesday at the World Health Assembly in Geneva that added to an initial $1 million pledge last week.

The outbreak, the most serious since the 2014 West Africa epidemic that killed more than 11,000 people, does not yet meet the criteria to be declared an international public health emergency, the World Health Organization said Friday.

But the WHO, in a statement, said “a vigorous response” from the international community is needed to prevent a sharp escalation in the outbreak.

The discovery of at least one case in Mbandaka, a densely populated port city on the eastern bank of the Congo River, has raised concerns about the potential for rapid spread of the disease, which had previously been limited to a remote area in the rain forest of Congo’s Equateur province.

As of late Friday, the Congolese health ministry reported four confirmed cases in the Mbandaka area.

At the World Health Assembly in Geneva today, WHO officials said there have been 51 confirmed or probable cases of Ebola in the outbreak, and 27 of those people have died.

Hundreds of people have been in contact with infected people and are being monitored, and they are candidates for the first round of an experimental vaccination campaign that began this week.

WHO officials estimate that outbreak-control efforts will cost $26 million over the next three months.

As of Friday, the WHO had received commitments for about $9 million.

“So we are about 17 million short,” Peter Salama, the WHO’s lead official in charge of epidemic response, said during a news conference in Geneva on Friday.

That may sound like a considerable amount, he said, but not compared with the Ebola epidemic in West Africa, which cost between $3 billion and $4 billion.