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.

Several airlines have already stopped flying to Guinea, Liberia and Sierra Leone - the countries worst affected by the world's most deadly outbreak of Ebola, which has no known cure.

It has killed 1,145 people this year, the World Health Organization says.

Security has been stepped up at health centres treating Ebola patients in Liberia

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.

'Greatest setback'

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.

Ebola Virus Disease (EVD)

• Symptoms include high fever, bleeding and central nervous system damage
• Fatality rate can reach 90% - but current outbreak has about 55%
• Incubation period is two to 21 days
• There is no vaccine or cure
• Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
• Fruit bats, a delicacy for some West Africans, are considered to be virus' natural host

Blood-stained mattresses, bedding and medical equipment were taken from the centre, a senior police officer told BBC News, on condition of anonymity.

"This is one of the stupidest things I have ever seen in my life," he said. "All between the houses you could see people fleeing with items looted from the patients."

The looting spree, he added, could spread the virus to the whole of the West Point area.

Health workers flee

Lindis Hurum, from medical charity Medecins Sans Frontieres (MSF), says there is an urgent need for a massive public awareness campaign in Liberia.

"Some people don't believe that it exists. Definitely, as the situation is getting worse and more people are getting sick, more people also start to believe it," she told the BBC.

"But they don't necessarily understand or know how they should prevent it."

MSF says the Ebola outbreak has had a terrible impact on Liberia's entire healthcare system, which it says is more or less falling apart.

Many health facilities have closed, with patients as well as medical staff, too scared to turn up for fear of catching the disease.

The Ebola epidemic began in Guinea in February and has since spread to Liberia, Sierra Leone and Nigeria.

One Nigerian doctor has survived the disease and was sent home on Saturday night, said Health Minister Onyebuchi Chukwu in a statement.

Mr Chukwu said five other people infected with Ebola had almost fully recovered.

The death toll of 1,145 was announced on Friday after the WHO said 76 new deaths had been reported in the two days to 13 August. There have been 2,127 cases reported in total.