South Africa's common law was rewritten on Thursday to classify forced anal sex with a woman or girl, previously considered indecent assault, as rape.

The country's Constitutional Court ruled that the distinction hitherto made between anal and vaginal violation of a female was unconscionable.

"The extension of the common law definition of rape to include non-consensual anal penetration of females will be in the interests of justice," reads a majority judgment by the highest court.

The court was giving judgment in the case of a 44-year-old man, Fanuel Masiya, convicted of raping a nine-year-old girl three years ago.

The girl was penetrated anally but a regional court ruled it rape -- even though the law classified the offence as indecent assault -- saying to do otherwise would be irrational and senseless.

The court made no ruling on non-consensual anal sex with men or boys, saying this went beyond the facts of the case before it.

"It is not desirable that a case should be dealt with on the basis of what the facts might be rather than what they are."

But it said those crimes were equally heinous and said the law may need to be changed later.

"It can hardly be said that the non-consensual anal penetration of males is less degrading, humiliating and traumatic."

Some 50,000 rapes, including around 20,000 of children, are reported to South African police every year, but women's groups say the real figure is around 1.5 million.

About 5.5 million people out of a total population of 47 million are believed to be HIV-positive.

The regional court magistrate in the Masiya case called the existing definition of rape archaic and discriminatory, and referred the case to a high court for sentencing, which has not yet happened. High courts in South African can impose harsher sentences than the lower courts.

The matter was subsequently referred to the Constitutional Court as the only body competent to rule whether laws were in line with the objectives of the country's constitution.

"The case raises constitutional issues of considerable public importance," the highest court's ruling said Thursday.

The trauma of anal rape was just as humiliating, degrading and physically hurtful as vaginal rape, and both forms of violation carried the threat of HIV infection, said the judgment.

The court described the prevalence of sexual violence in South African society as "deeply troubling," and said changing the definition would "express the abhorrence with which our society regards these pervasive but outrageous acts."

The court changed Masiya's conviction to one of indecent assault, saying the new definition would not apply retrospectively.

AP