HIV-positive Indians have been campaigning for better healthcare
Some 90% of gay men in the Asia-Pacific region are denied access to HIV/Aids help because of discriminatory laws in many states, a UN-backed report says.
Almost half the region's countries criminalise gay male sex and the report says this is worsening a situation in which infection rates are climbing.
Repressive laws "often take on the force of vigilantism", it argues.
Governments were urged to reform legal systems and policing to ensure an effective response to the crisis.
The report, produced jointly by the UN Development Programme and the Asia Pacific Coalition on Male Sexual Health, noted that several countries including Nepal, India, the Philippines and South Korea had brought in new laws and policies to address the problem.
"However, these are exceptional developments and action is required to improve the legal environment in all countries," it added.
The report said the high-risk group, which includes homosexuals and bisexuals, can potentially account for between 10 and 30% of new HIV infections in a typical Asian country.
Nineteen out of 48 countries in the region criminalised male-to-male sex and these laws often led to abuse and human rights violations, it said.
Punishments for sex between men ranged from the death penalty in Afghanistan and north-west Pakistan to whipping in Malaysia and Indonesia's Aceh region, the report found.
Even if punishments were not enforced, they provided the basis for extortion, harassment and violence, it said.
Police enforced public order and prostitution laws selectively against gay men in some countries, the report went on.
In Sri Lanka and the Philippines, for example, vagrancy laws were used in this way, the report said.
Another abuse reported in countries such as Thailand and India was the confiscation of condoms as evidence of illegality.
In China and Singapore, the report found, HIV education materials were censored.
"The effectiveness of the HIV response will depend not just on the sustained scale up of HIV prevention, treatment and care, but on whether the legal and social environment support or hinder programmes for those who are most vulnerable," the UNDP's Mandeep Dhaliwal said in a statement.