A health official says a senior doctor working at Liberia's largest hospital has died of Ebola.

Tolbert Nyenswah, an assistant health minister, said Dr. Samuel Brisbane died Saturday at an Ebola treatment center on the outskirts of the capital, Monrovia.

He is the first Liberian doctor to die in an outbreak the World Health Organization says has killed 129 people in the country.

The WHO says the outbreak, the largest ever recorded, has also killed 319 people in Guinea and 224 in Sierra Leone.

Health workers are at serious risk of contracting the disease, which spreads through contact with bodily fluids.

Sierra Leone's top Ebola doctor fell ill with the disease last week, and the aid group Samaritan's Purse said Saturday that an American doctor in Liberia was also sick.