(Reuters) - Members of an NBC News crew who worked with a cameraman who contracted Ebola in Liberia have been quarantined, New Jersey health officials said on Saturday.

Officials said the order was issued late Friday after the crew members violated an agreement to voluntarily confine themselves. They said none of the team has exhibited symptoms of the often fatal disease since returning from Liberia, one of three West African countries at the epicenter of the outbreak.

Meanwhile, the condition of the freelance American cameraman continued to improve. At Nebraska Medical Center, Ashoka Mukpo, 33, has received the experimental drug Brincidofovir and a blood transfusion from Dr. Kent Brantly, who earlier recovered from a bout with Ebola at Emory University Hospital in Atlanta. Brantly also contracted the disease in Liberia.

Mukpo "is eating some solid food now, so we're still headed in the right direction," said Dr. Phil Smith, director of the biocontainment unit at Nebraska Medical Center.

The death this week of the first person diagnosed with Ebola in the United States has increased fears that the disease could spread outside West Africa, where it has killed more than 4,000 people. U.S. health authorities are stepping up efforts to stop the spread of the deadly virus.

Medical teams at New York's John F. Kennedy Airport, armed with Ebola questionnaires and temperature guns, began screening passengers who traveled from Liberia, Sierra Leone and Guinea on Saturday.

The NBC News crew had agreed with health officials to stay in their homes after returning to the United States but then failed to do so, Donna Leusner, a spokeswoman for the New Jersey Department of Health, said in a statement.

The mandatory quarantine will ensure the group remains confined until Oct. 22, the end of a 21-day maximum incubation period for Ebola, Leusner said.

"The NBC crew remains symptom-free, so there is no reason for concern of exposure to the community," she said.

NBC News has reported that the crew that worked with Mukpo included its medical correspondent Dr. Nancy Snyderman.

The spokeswoman declined to provide additional details about the crew, its size and the specific reasons behind the mandatory order, citing patient privacy.

(Reporting by Letitia Stein in Tampa, Florida, and Alex Dobuzinskis in Los Angeles; Editing by Frank McGurty and Raissa Kasolowsky)