US health officials will actively monitor health workers who have treated Ebola patients in West Africa, under new rules.

Updated guidelines issued on Monday will require most medics to be checked for symptoms for 21 days but will not require quarantine or isolation.

The UN Secretary General has condemned enforced quarantine measures. The current Ebola outbreak in West Africa has infected more than 10,000 people and killed almost 5,000.

The US announcement comes after a nurse who complained about her quarantine in New Jersey was allowed to return home.

Defying the new guidelines, New Jersey Governor Chris Christie defended the mandatory isolation imposed on Kaci Hickox as she returned home from Sierra Leone.

He added: "That's what we will continue to do. His stance conflicts with UN Secretary General Ban Ki-moon, who earlier said those seeking to help in affected areas "should not be subjected to restrictions that are not based on science".

"Those who develop infections should be supported, not stigmatised." People are not contagious until they develop Ebola symptoms.

Three US states including New Jersey had said they would require a 21-day quarantine for all health workers who have had contact with Ebola patients. The move came in response to a New York doctor who fell ill with the Ebola virus last week, the morning after he had travelled on the subway and been bowling.

On Monday, the US Centers for Disease Control and Prevention (CDC) issued fresh guidance for travellers and health workers returning from West Africa, where the outbreak has claimed more than 4,000 lives.

It set out four risk categories, and put most healthcare workers returning from the epidemic-hit region as at "some risk" of infection.

CDC director Dr Tom Frieden said workers considered to be at high risk or some risk would be required to be "actively" monitored for symptoms for 21 days. Those at highest risk are anyone who's had direct contact with an Ebola patient's body fluids.

Even if they have no symptoms, they should avoid commercial travel and large public events, Dr Frieden said, adding that voluntary quarantine was enough.

Kaci Hickox was working with Medecins Sans Frontieres (MSF) in Sierra Leone before her return to the US.

Ms Hickox said she was made to feel like a criminal after being quarantined in Newark as she returned from Sierra Leone last Friday.

She was released on Monday and flown back to her home in Maine.

The New Jersey health department said Ms Hickox had tested negative for Ebola on Saturday and had been free of symptoms for 24 hours.

Mr Christie defended his state's quarantine procedures and said that Ms Hickox had arrived in the US with a temperature - something the nurse denies.