A US doctor working with Ebola patients in Liberia has tested positive for the deadly virus.

Relief organisation Samaritan's Purse says Kent Brantly, aged 33, is being treated at a hospital in the capital, Monrovia.

Brantly is the medical director for the aid organization's case management center in the city.

He has been working with Samaritan's Purse in Liberia since October 2013 as part of the charity's post-residency program for doctors, said the group's spokeswoman Melissa Strickland.

The organization's website says he had worked as a family practice physician in Fort Worth, Texas.

Strickland says that Brantly's wife and children had been living with him in Africa, but they are currently in the US.

Robert Earley, president and CEO of the JPS Health Network said: "There’s an incredible level of braveness in Kent. You don’t meet people like this every day."

Dr Brantley reportedly recognized the symptoms and had confined himself in an isolation ward.

He followed safety protocols strictly when he was treating patients, and investigations are being carried out as to how he contracted the disease.

The highly contagious disease has killed almost 700 people in West Africa since the outbreak began earlier this year. Ebola outbreaks can have a case fatality rate of up to 90%, although the fatality rate of the current outbreak is lower at around 60%.

Patients suffer from vomiting and diarrhea as well as internal and external bleeding.

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

A senior doctor working at Liberia’s largest hospital has died of Ebola. Tolbert Nyenswah, an assistant health minister, said Dr Samuel Brisbane died on Saturday at an Ebola treatment centre on the outskirts of the capital, Monrovia.

He is the first Liberian doctor to die in an outbreak the World Health Organisation (WHO) 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.

Sierra Leone’s top Ebola doctor fell ill with the disease last week.