Following earlier denials, Liberia has admitted that 17 suspected Ebola patients are “missing” after a health centre in the capital was looted.
The government had sought to reassure people, saying all the patients had been moved to another health facility.
But Information Minister Lewis Brown told the BBC that 17 inmates had gone “back into their communities”.
The World Health Organization (WHO) has called for exit screenings on all travellers from affected countries.
It wants checks at airports, sea ports and major land crossings.
More than 400 people are known to have died from the virus in Liberia, out of a total of 1,145 deaths recorded in West Africa by the World Health Organization this year.
Assistant Health Minister Tolbert Nyenswah said protesters in the West Point district attacked a quarantine centre on Saturday because they were unhappy that patients were being taken there from other parts of the capital, Monrovia.
Other reports suggested the protesters had believed Ebola was a hoax and wanted to force the centre to close.
Mr Nyenswah had said that all the suspected patients had been transferred to an Ebola treatment centre in the John F Kennedy Memorial Medical Center in Monrovia.
But on Monday, the information minister said 17 of the 37 patients were unaccounted for.
He said the authorities were now trying to track them down but said he was confident they would return.
“Most of the people that went into this holding facility came there voluntarily,” he told the BBC.
“So our impression is that they still want to be [there], but they were forcibly removed by vandals and looters, not because they wanted to leave; so we are sure that they will return.”
He said the attack on the quarantine centre was Liberia’s “greatest setback” since the Ebola outbreak began.