MONROVIA, Liberia — Authorities in Liberia urgently searched on Monday for 17 people who fled an Ebola medical center over the weekend when it was attacked by looters who stole blood-stained sheets and mattresses and took them into an enormous slum.

Health officials were combing Monrovia’s West Point area that is home to at least 50,000 people to try to stop the virus from spreading further in a country where more than 400 people already have died.

The World Health Organization on Monday urged Liberia and other Ebola-affected countries to screen all passengers leaving international airports, sea ports and major ground crossings.

Those with symptoms of the virus also were urged not to travel. Many airlines have halted services to the capitals of Liberia and neighboring Sierra Leone.

The weekend chaos in Monrovia highlights the growing unease and panic in Liberia amid the mounting Ebola death toll and illustrates the risks of further instability in this deeply impoverished country where mistrust of the government runs high. In addition, health workers are complaining about a lack of protective gear. Treatment centers are viewed by many as a place where people go just to die.

“They are not happy with the way Ebola is being managed and the response that the government is providing,” said Koala Oumarou, a director for the aid group Plan Liberia, which is helping the health ministry to raise awareness. “It’s where the frustration is coming from.”

Liberia’s president already has declared a state of emergency, dispatching armed soldiers to enforce quarantines of infected areas. But little was done Saturday to stoop looters from invading the Ebola quarantine center and taking items covered in bodily fluids that now could only further transmit the gruesome virus, witnesses said. Ebola is spread through direct contact with the blood, vomit, feces or sweat of sick people.

Witnesses say an angry mob attacked the West Point facility, a “holding center” for people who had been exposed to Ebola and were being monitored during an incubation period for signs of the disease. The looters took medical equipment, and mattresses and sheets that had bloodstains, said a senior police official, who insisted on anonymity because he was not authorized to speak to journalists.

“All between the houses you could see people fleeing with items looted from the patients,” the official said, adding that he now feared “the whole of West Point will be infected.”

Witnesses said the weekend mob was angry about possible Ebola patients being brought into their area.

None of those who fled had yet been confirmed to have Ebola