A leading doctor who risked his own life to treat dozens of Ebola patients died on Tuesday from the disease, officials said, as a major regional airline announced it was suspending flights to the cities hardest hit by an outbreak that has killed more than 670 people.

Dr Sheik Humarr Khan, who was praised as a national hero for treating the disease in Sierra Leone, was confirmed dead by health ministry officials there. He had been hospitalized in quarantine.

Health workers have been especially vulnerable to contracting Ebola, which is spread through bodily fluids such as saliva, sweat, blood and urine. Two US health workers are currently hospitalized with Ebola in neighboring Liberia.

The Ebola outbreak is the largest in history with deaths blamed on the disease not only in Sierra Leone and Liberia, but also Guinea and Nigeria. The disease has no vaccine and no specific treatment, with a fatality rate of at least 60 percent.

Binyah Kesselly, chairman of the Liberia Airport Authority board, said police are now present at the airport in Monrovia to enforce screening of passengers.

'So if you have a flight and you are not complying with the rules, we will not allow you to board," he said.

In a statement released on Tuesday, airline ASKY said it was temporarily halting flights not only to Monrovia but also to Freetown, Sierra Leone. Flights will continue to the capital of the third major country where people have died - Guinea - though passengers departing from there will be "screened for signs of the virus".

Passengers at the airline's hub in Lome, Togo, also will be screened by medical teams, it said.

"ASKY is determined to keep its passengers and staff safe during this unsettling time," the statement said.

The measures follow the death on Friday of a 40-year-old US man of Liberian descent, who had taken several flights on ASKY, causing widespread fear at a time when the outbreak shows no signs of slowing in West Africa.

Patrick Sawyer, who worked for the West African nation's Finance Ministry, took an ASKY Airlines flight from Liberia to Ghana, then on to Togo and eventually to Nigeria where he was immediately taken into quarantine until his death.

The World Health Organization said the risk of travelers contracting Ebola is considered low because it requires direct contact with bodily fluids or secretions such as urine, blood, sweat or saliva. Ebola can't be spread like flu through casual contact or breathing in the same air.