Ebola scare in the US
Students leave Tasby Middle School over fears of contact with the Ebola virus in Dallas, TexasMike Stone/Reuters

US officials have placed four members of a family in Texas under armed guard because they had direct contact with a Liberian national stricken with the Ebola virus, while as many as 100 others in the state are being monitored for suspected exposure.

Among the four, who are being held in a Dallas apartment, is the girlfriend of Liberian national Thomas Eric Duncan, who remains in a critical condition at Texas Health Presbyterian Hospital.

Up to 100 people might have had direct or indirect contact with Duncan, said Dr Thomas Frieden, director of the US Centers for Disease Control and Prevention (CDC).

The Department of State Health Services spokeswoman Carrie Williams told BBC the list includes individuals "who have had even brief encounters with the patient or the patient's home".

"The number will drop as we focus in on those whose contact may represent a potential risk of infection," Williams said.

According to officials, between 12 and 18 people are suspected to have had direct contact with Duncan, and this includes five school-age children.

The Ebola epidemic in West Africa has so far killed at least 3,300 people. The latest estimate by the World Health Organisation (WHO) says more than 7,000 people have been diagnosed with the virus.

While authorities face criticism over a series of alleged missteps in handling the case - the first diagnosis of the deadly virus in the country - it emerged that another US national was infected in Liberia and was being flown home for treatment.

An unnamed 33-year-old American freelance television cameraman working for NBC News in Liberia will be flown home.

The TV network said the cameraman quarantined himself after he started feeling ill and contacted Doctors Without Borders.

The network's entire crew in Liberia will be flown back to the US on a private charter plane and will be placed under a 21-day quarantine.

Health officials faced criticism over the delay in sealing the apartment where Duncan stayed and disposing of the materials, including sweat-ridden bed sheets he used.

However, Dallas County officials said none of those thought to have had contact with the Liberian was showing symptoms of Ebola, Reuters reported.

It also emerged that Duncan, who contracted the virus while transporting a pregnant woman who later died of Ebola, had withheld information about his contact with patients.

Liberian airport authorities said Duncan would be prosecuted for denying he had contact with an Ebola patient.