In Liberia’s capital of Monrovia, taxis filled with families crisscross the city, searching in vain for a facility with space to treat loved ones infected with the Ebola virus. Children orphaned by the disease and shunned by other relatives have nowhere to go. The government’s main hospital is plagued by floods and electrical fires, and several employees have succumbed to Ebola.

That grim picture, detailed Monday by the World Health Organization, is poised to become even bleaker. The number of Ebola cases in Liberia, the country hit hardest by the outbreak, is “increasing exponentially,” the agency said, adding that the country’s needs “have completely outstripped the government’s and partners’ capacity to respond.”

The WHO’s description of the situation in Liberia echoed the warnings of aid groups such as Doctors Without Borders: that the outbreak is accelerating rapidly and slipping further out of control by the day. In Liberia, thousands of new cases are expected in coming weeks, the agency said.

A team of emergency experts dispatched by the WHO to assess the situation in Liberia recently found a country overwhelmed by the crisis.

“As soon as a new Ebola treatment facility is opened, it immediately fills to overflowing with patients, pointing to a large but previously invisible caseload,” the WHO wrote in its assessment Monday. “When patients are turned away at Ebola treatment centers, they have no choice but to return to their communities and homes, where they inevitably infect others.”

When a treatment center was hastily set up by the WHO for Liberia’s health ministry, for example, it had room for 30 patients but received more than 70 as soon as the doors opened. In Montserrado County, where Monrovia is located, the WHO estimated the need for treatment beds at 1,000; only 240 exist.

It remained unclear when and how more Ebola treatment facilities would be established and who might be willing to staff them. The WHO said Monday that it would continue to push for more aid in Liberia and the other affected countries — Guinea, Sierra Leone, Nigeria and Senegal — and that it would “hold the world accountable for responding to this dire emergency with its unprecedented dimensions of human suffering.”

The world appears to be responding, albeit slowly.

The Pentagon announced on Monday that it would set up a 25-bed field hospital in Liberia to help provide medical care for health workers responding to the epidemic. A Defense Department representative said the $22 million hospital is being provided at the request of the U.S. Agency for International Development, which is coordinating the U.S. response.

Defense Department personnel will not be permanently stationed at the facility, and after the hospital is established, it will be transferred to the government of Liberia, the representative said. The news marked a first step in President Obama’s pledge over the weekend to use U.S. military assets to fight the outbreak in West Africa.

The British government said Monday it planned to set up an Ebola treatment center in Sierra Leone. The 62-bed facility will be built and operated by British military engineers and medical staffers and will be near the capital of Freetown. It should be operational within eight weeks, government officials said.

Meanwhile, further pledges of assistance from other world governments are expected this week. But questions remain about when such help might arrive and whether it will come in time to halt the sharply rising number of infections. (Late Monday, Emory University Hospital in Atlanta said it will treat a third patient infected with the virus, but it did not provide additional details.)

The Ebola epidemic over time

In an interview Sunday from Brussels, Brice de le Vinge, the operations director for Doctors Without Borders, the humanitarian group that has been the most active in the region since the outbreak early this year, said the situation in Liberia remains untenable.

“We are overstretched physically, and we have people dying at our doorsteps every day,” he said.

Caitlin Ryan, a field communications officer for Doctors Without Borders, said Ebola victims continue to turn up dead daily outside the gates of its 160-bed facility in Monrovia, some having died during the car ride there.

Workers regularly turn away patients because of a lack of beds, sending them home with only a kit containing chlorine spray, masks, gowns and gloves, in the hope of protecting family members and other caregivers.

Ryan said some desperate parents abandon their sick children at the hospital’s front gate, “because they know we are much more likely to take a small child.”

Lenny Bernstein and Lena Sun contributed to this report.