Tia Phalla, of Cambodia's National AIDS Authority, said the country's so-called 100 percent condom use programme, which provides sex education and distributes condoms to sex workers, "is facing difficulties" because of a new anti-sex trafficking law and lack of financial support.
Police began a crackdown on brothels after the new law was passed in February, which has reportedly forced prostitutes to leave condoms behind as they move from place to place.
"Enforcement of the anti-trafficking law harms the 100 percent condom use in brothels," Tia Phalla told a three-day national AIDS conference in Phnom Penh.
The percentage of sex workers who consistently used condoms with clients had already begun to drop to 94 percent in 2007 from 96 percent in 2003, according to AIDS authority data.
Additionally, only six of the country's 24 provinces and cities currently have funds to carry out the programme, Tia Phalla said.
"The main risk of a second wave of HIV infections occuring in Cambodia is from female sex workers, their clients and sweethearts," said a statement by the AIDS authority.
Before the 100 percent condom use programme began, Cambodia's overall HIV rate was the worst in the region, peaking at 3.7 percent of the population in 1997. Rates among prostitutes were estimated at 40 percent.
The aggressive condom and sex education campaign is believed to have helped drop Cambodia's overall HIV prevalence to 0.9 percent.