But the CDC also said it was "strongly" encouraging the use of condoms as a precaution against the virus that causes AIDS.

Recent studies have suggested that the use of hormonal contraceptives could increase the risk of women contracting HIV. But after reviewing the studies, the Atlanta-based CDC said, "the evidence does not suggest" a link between oral contraceptives such as the birth control pill and increased HIV risk.

For injectable forms of birth control such as Depo-Provera the evidence is inconclusive, but in the absence of more definitive research it too is considered safe, CDC officials said.

Women at risk for HIV infection or who already have the virus "can continue to use all hormonal contraceptive methods without restriction," the CDC said.

The World Health Organization reached a similar conclusion last February.

"It's hard to conclusively say whether or not there is an increased risk," from hormonal contraceptives, Dr. Naomi Tepper, a CDC medical officer, told Reuters.

"Because we can't say from the evidence that there is an increased risk, they are all still considered safe, including the injectables."

The studies are particularly confusing with women who use progesterone-only injectables, which in the United States is sold under the brand named Depo-Provera, Tepper said.

A study published last October in The Lancet Infectious Diseases journal suggested that hormonal contraceptives, primarily the injectable forms, could double the risk of women contracting HIV.

For women who already have the disease, hormonal contraceptives could double the risk of transmitting the virus to a partner, according to the study. But Tepper said it was unclear why the contraceptives could increase risk of HIV infection.

The CDC said Thursday that all women at risk of contracting HIV and particularly those using the injectable forms of hormonal birth control, should make sure their partners use condoms as a safeguard against HIV infection.

"All women, if they don't want to become pregnant should be using an effective method of contraception," Tepper said. "And they also should be using something to protect against HIV or sexually-transmitted infections."

In 2010, 10,000 women in the United States were infected with HIV, the CDC said.

Pregnancy can also be medically risky for women with HIV and the disease can be transmitted to the unborn child, the CDC said.

(Editing by Tom Brown and Paul Simao)

• A Permanent Economic Emergency