Gay and transgender rights groups barred from a major UN AIDS conference opening Wednesday plan to defy the decision by joining other delegations at the meeting on ending the HIV epidemic.

Twenty-two groups were denied UN accreditation to attend the gathering after Russia, the Organization of Islamic Cooperation, Cameroon and Tanzania raised objections, drawing outrage from AIDS activists.

Of the 22 barred groups, 16 will join government and civil society delegations, leaving only six that will not be represented, said UNAIDS executive director Michel Sidibe.

"This meeting should be about inclusiveness," Sidibe told AFP in an interview.

"This meeting should be about the debate for ending stigma and discrimination and reaching people who have not been reached by our programs," he said.

The United States will include the US-based Global Action for Trans Equality in its official delegation, the US mission to the United Nations confirmed.

US Ambassador Samantha Power and her EU counterpart Joao Vale de Almeida had formally protested the decision to shut the door on some groups in letters to General Assembly president Mogens Lykketoft.

"Given that transgender people are 49 times more likely to be living with HIV than the general population, their exclusion from the high-level meeting will only impede global progress in combatting the HIV/AIDS pandemic and achieving the goal of an AIDS-free generation," Power wrote in a letter sent last month.

Despite the push to find a place for the barred groups, four from Cameroon and two from Russia will not be attending, a UN official said.

"We don't support exclusion," Sidibe said. "We know that we will never win by making them silent."

Secretary-General Ban Ki-moon will open the conference during a ceremony attended by Nelson Mandela's grandson, Ndaba Mandela, whose father Magkatho died of AIDS in 2005.

He was Mandela's last surviving son.

The HIV epidemic has been forced into decline over the past decade, but about 36.7 million people worldwide are living with HIV/AIDS, most of them in sub-Saharan Africa.

Some 17 million people have access to antiretroviral therapy, but the UN meeting will aim to fast-track treatment and prevention to end AIDS by 2030.