VIENNA (Reuters) - U.N. Secretary-General Ban Ki-moon warned on Monday against "unnecessarily" strict restrictions on the movement of health workers who have been fighting the deadly Ebola virus in West Africa.

In some U.S. states officials have imposed quarantines on health professionals returning from three Ebola-ravaged West African countries, but the U.S. federal government opposes such measures.

Canada and Australia have barred entry for citizens from Liberia, Sierra Leone and Guinea, where the disease is widespread, and some U.S. politicians have called for a similar ban by the United States.

"The best way to stop this virus is to stop the virus at its source rather than limiting, restricting the movement of people or trade," Ban told a news conference in Vienna. "Particularly when there are some unnecessarily extra restrictions and discriminations against health workers."

"They are extraordinary people who are giving of themselves, they are risking their own lives."

Major international airlines and shipping service lines should continue normal trade, movement and transportation, he said.

Medical experts say Ebola is difficult to catch and is spread through direct contact with bodily fluids from an infected person and is not transmitted by asymptomatic people.

"Of course, when somebody has a symptom (of Ebola) those people should be immediately treated and supported and evacuated when necessary," Ban said.

The most deadly outbreak of Ebola on record has killed nearly 5,000 people, all but a handful of them in Liberia, Guinea and Sierra Leone.

(Reporting by Shadia Nasralla and Fredrik Dahl; editing by Ralph Boulton)