A mass HIV outbreak in a Cambodian village was most likely caused by contaminated medical equipment, the World Health Organization and Cambodian health ministry said Saturday.

Hundreds of panicked residents of the remote Roka village in western Battambang province have flocked for testing since news of the infections first emerged in late November.

An unlicensed Cambodian doctor has been charged with murder after he admitted reusing needles and syringes at his clinic.

A joint study carried out by the WHO and the health ministry found 212 people have now been found to be carrying the virus out of 1,940 people tested so far -- with contaminated equipment the most likely cause.

"The study showed that the percentage of people that reported receiving an injection or intravenous infusion as part of their health treatment was significantly higher among the people who tested positive for HIV than the people who were HIV negative," a joint statement said.

Researchers added that other potential transmission routes -- such as unprotected sex, drug use and mother-to-child transmission -- had been ruled unlikely.

At least 174 of those with HIV -- including 39 people aged 14 or younger and 46 people aged 60 years old or older -- are from Roka village.

Yem Chroeum, a 55-year-old self-styled doctor, admitted reusing needles and syringes on different patients, police said.

Alongside murder, Yem Chroeum has also been charged with deliberately infecting people with HIV and operating an unlicensed clinic.

He faces a maximum sentence of life imprisonment.

Cambodia's Health Minister Mam Bunheng called on medical staff to "use clean and sterile equipment".

"We have reinforced implementation of the Ministry of Health policy to stop unlicensed informal medical practices," he said in the statement.

The outbreak first came to the authorities' attention in late November when a 74-year-old Roka man tested positive at a local health centre for the virus.

His grand-daughter and son-in-law also tested positive soon afterwards, according to the health ministry.

Cambodia has been widely hailed for its efforts in tackling HIV/AIDS.

The National AIDS Authority says the rate of HIV infection among people aged 15 to 49 has declined from 0.6 percent in 2013 to 0.4 percent in 2014.

Currently, Cambodia estimates more than 73,000 people live with the illness.

The country is aiming to stamp out new HIV/AIDS infections by 2020.