West African nations affected by the worst-ever outbreak of Ebola have been urged to screen "all people at international airports, seaports and major land crossings" in order to stop its spread.

The World Health Organization said on Monday that authorities should stop anyone with signs of the virus from travelling, days after it warned that the magnitude of the outbreak was "vastly underestimated".

The WHO reiterated that the risk of getting infected with the virus on an aircraft was small and there was no need for wider travel or trade restrictions.

"Any person with an illness consistent with Ebola should not be allowed to travel unless the travel is part of an appropriate medical evacuation," the UN agency said.

Cameroon meanwhile closed all its land, sea and air borders with Nigeria in a move to prevent the spread of the disease, a government spokesman told the AFP news agency on Monday.

No cases of Ebola have been recorded in Cameroon, which shares a 2,000km border with Nigeria, where the virus has killed four people and infected about a dozen others.

The outbreak in West Africa has already killed 1,145 and infected more than 2,000.

Fears of worsened Liberia outbreak

The WHO's latest statement came as Liberian authorities were trying to find 17 Ebola-infected patients who fled a quarantine center on Sunday in West Point, Monrovia, after it was looted by an armed gang.

The Associated Press quoted the country's assistant health minister Tolbert Nyenswah as saying that some of the patients were found and were being monitored at a hospital. It was not clear how they were identified.

However, the AFP quoted the country's information minister, Lewis Brown, as saying they had not been found, and the gang which looted the facility "took away mattresses and bedding that were soaked with fluids from the patients".

The virus spreads through bodily fluids.

The authorities are now considering sealing off the area, which is home to around 75,000 people.

"All those hooligans who looted the center are all now probable carriers of the disease," said Brown. "To quarantine the area could be one of the solutions."

PHOTO CAPTION

Public health advocates stage an Ebola awareness and prevention event on August 18, 2014 in Monrovia, Liberia.

Aljazeera