A group of 51 Muslim countries has blocked LGBT rights organisations from attending a United Nations conference on Aids next month.
Egypt, representing the Organization for Islamic Co-operation, wrote to the General Assembly president to object to the participation of 11 groups.
US, EU, and Canadian officials have written to the president of the 193-member organisation in protest.
Egypt’s representatives did not give a reason for requesting the ban.
US Ambassador Samantha Power said the groups appeared to have been chosen for their involvement in gay or transgender causes.
“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 combating the HIV/Aids pandemic,” Mrs Power wrote to general assembly president Mogens Lykketoft.
She added that efforts to block participation of nongovernmental organisations (NGOs) is becoming “epidemic” and this severely damaged the credibility of the UN.
Some of the banned groups include the Asia Pacific Transgender Network from Thailand, the Eurasian Coalition on Male Health from Estonia, and the Ishtar Men Who Have Sex With Men from Kenya.
Other vetoed groups were due to come from Guyana, Jamaica, Peru and Ukraine.
General Secretary Ban Ki-moon announced in 2014 that the UN would begin recognising the same-sex marriages of its staff. Russia, with the support of 43 nations, including India, Egypt, China, and Pakistan attempted to overturn that decision.
In a press release to announce the conference, UN officials “emphasised the need to reach the people most affected by HIV, who continue to be left behind in the Aids response including sex workers, men who have sex with men, transgender people and people who inject drugs”.
The conference, which will take place in New York in early June, has the objective of ending the Aids epidemic by 2030.