CAIRO — As the coronavirus epidemic sweeps through Yemen, rebels who control the north of the country have been threatening medical workers to keep them quiet, part of an effort to cover up the true toll of the outbreak, humanitarian officials say.

In southern Yemen, ill-equipped hospitals are turning away patients with coronavirus symptoms, leaving them uncounted and at risk of dying at home, say international aid workers, local health officials and postings on social media.

The result is an outbreak health experts say is dramatically larger than the almost 400 cases and 87 deaths reported by official sources as of Wednesday.

Doctors and aid workers say they believe that thousands of Yemenis are being infected every week and hundreds are dying. Yemenis have flooded Facebook and other social media with death condolences in recent weeks, filling their pages with “electronic obituaries,” said one United Nations worker.

“We are just seeing the tip of the iceberg,” said Caroline Seguin, Yemen operations manager for the medical charity Doctors Without Borders, the only nongovernmental group treating coronavirus patients in the country.

In the worst-case scenario, the virus could ultimately infect about 28 million Yemenis — nearly the entire population — and cause at least 65,000 deaths, Altaf Musani, the World Health Organization’s representative, told the Lancet medical journal last week.

Weeks ago, epidemiologists warned that the virus could spread farther and faster in the Arab world’s poorest nation than in many other countries. But the reported case numbers remain deceptively low.

The northern rebels, known as the Houthis, have sought to hide the extent of the epidemic by threatening to arrest or kill doctors and journalists if they discuss the outbreak, and ordering the secret burial of those suspected of dying of covid-19, according to aid workers, U.N. employees and local doctors.

They also report that armed militiamen have been sent to the homes of people who have fallen ill. People are now too scared to report illness.

In the south, controlled by various armed groups, hospitals and clinics are turning away patients displaying coronavirus symptoms because of overcrowded wards and lack of trained staff and equipment, said U.N. experts and aid workers. Other facilities have closed because health workers are afraid to work without adequate personal protective gear and testing kits.

Deaths are mounting in the main southern city, Aden, with about 8o every day, a sevenfold increase over the normal death toll earlier this spring, according to Doctors Without Borders. In one week last month, at least 385 people in Aden died of ­coronavirus-like symptoms, said the charity Save the Children.

Long before the coronavirus emerged, Yemen was already ­being called the world’s worst humanitarian crisis, with at least 10 million people on the edge of famine. On Tuesday, a U.N. appeal for countries to fund emergency programs in Yemen fell far short of its goal, raising the prospect that programs to address the coronavirus epidemic could be slashed within weeks. Starvation, poverty and a litany of diseases have left Yemenis particularly vulnerable to the ravages of covid-19.

“There are preliminary reports from the isolation units that point to exceptionally high case-fatality rates,” said Lise Grande, the United Nations’ top humanitarian official in Yemen. “Although we don’t have strong enough testing and a strong enough information base, the rate indicates it could be more than double what it is in other countries.”

Rebel intimidation

In the capital, Sanaa, a sign posted on a wall of the city’s largest and best-known burial ground reads: “Dear relatives of the deceased, we assure you that Khozaimah cemetery is full.”

Yet the Houthi authorities have reported just four coronavirus cases and one death in their area, which accounts for more than two-thirds of the country’s population.

Rebel health officials strictly control coronavirus testing, releasing results only if they are negative, said international aid officials who spoke on the condition of anonymity to avoid being targeted by the Houthis.

On Twitter and Facebook, Yemenis in Houthi-controlled areas have posted accounts of sending relatives with covid-19 symptoms to hospitals and never hearing from them again. Authorities did not permit the family members to retrieve the bodies of the deceased or inform them that the government had buried them. Yemenis have posted videos purportedly showing health workers, in white or green protective suits, secretly burying those thought to have died of the disease.

Doctors and nurses in the north have been detained, and others have had their phones taken away to prevent them from discussing the epidemic, according to aid workers and social media postings.

In some cases, armed escorts have accompanied health teams to the homes of suspected cases, rounding up the sick and their relatives at gunpoint to take them to isolation areas, according to aid workers and accounts on social media.

While the social media postings could not be confirmed, international aid groups and U.N. workers say they have heard similar accounts from their staff and other contacts on the ground.

 “People are sick and dying, and people are scared to death,” said a senior aid official speaking on the condition of anonymity to talk freely. “They are scared because they fear retaliation by security forces if they are suspected of being covid-positive.”

It is unclear why case numbers would be suppressed by the Iran-aligned Houthis, who for the past five years have been fighting a U.S.-backed coalition of Sunni Muslim countries led by Saudi Arabia that is seeking to restore Yemen’s government.

Some aid workers and political analysts said the rebels are worried that they could be forced to order a lockdown, denying them tax revenue or preventing them from attracting recruits to fight in the war. Others said the rebels are concerned that Yemenis would rise up against them for allowing the virus to take root.

 A Houthi political official and a spokesman for the rebels’ health ministry did not respond to a request for comment.

In a statement Friday, the Houthi health ministry criticized methods used by many countries to confront the disease, saying they “weakened the morale of their citizens and created a state of fear and anxiety.” Dealing with infections “as numbers and statistics” in many countries has “negatively affected people psychologically and weakened their immune systems,” the ministry said.

'Dying at home'

With hospitals and clinics destroyed by the war and an economic blockade causing shortages of medicine and medical equipment, only half of Yemen’s medical facilities are operational today, according to U.N. officials and aid workers. And only a fraction of them can handle covid-19 cases, they say.

There are about 700 intensive care beds and 500 ventilators to serve the population of roughly 30 million, according to Save the Children. There are also dire shortages of protective masks and gowns.

Some patients with covid-19 symptoms have been refused treatment at health facilities, according to aid groups and local health officials. That leaves patients with no choice but to return home and potentially spread the virus to others in their communities, which include camps and schools crowded with refugees.

“This is due to the fear of transmission among heath-care workers, and they refuse to deal with patients,” said Sheikh Alshoteri, a physician who specializes in infectious disease and sits on Yemen’s National Scientific Committee to combat the virus. “So they return back home and await death silently.”

In Taiz, Yemen’s third-largest city, hospitals are reporting dozens of cases of patients with covid-19 symptoms each week, said Rajah Almoliki, a physician and the city’s health office director. Most facilities do not have enough protective gear, and there are only 11 ventilators in the city of more than 600,000.

In Aden, the covid-19 treatment center run by Doctors ­Without Borders highlights the challenges facing the nation. As of last week, there had been 220 admissions of patients with covid-19-like symptoms and 99 deaths.

Most patients are arriving with “acute respiratory distress syndrome,” suggesting to doctors that many more people are sick at home. Unable to afford travel costs, many Yemenis go to hospitals only when their illness becomes severe.

“People are coming to us too late to save, and we know that many more people are not coming at all,” Seguin said. “They are just dying at home.”

The Doctors Without Borders center has also been treating many infected health-care workers, including 40 members of its own staff.

Yet even as the virus has been spreading, funding shortages have been forcing U.N. agencies to close down humanitarian programs, reduce health services at many hospitals and stop paying salaries of thousands of health workers.