Authorities in the Russian capital on Thursday refused to sanction the nation's first ever gay parade, saying that widespread public intolerance could trigger riots, but the parade organizers pledged to go ahead with the rally.

The parade's main organizer Nikolai Alexeyev said the city authorities' refusal to allow the parade was illegal and promised to challenge it in court. "The authorities decision is a violation of the Russian constitution," Alexeyev said.

The parade is scheduled to take place in the city center on May 27, the 13th anniversary of the decriminalization of homosexuality in Russia. "The parade will take place as scheduled, we won't cancel it," Alexeyev told The Associated Press.

The Moscow city government said Thursday it couldn't authorize the rally, saying it could draw a "negative reaction against its participants and trigger protests that could lead to violation of the public order and mass riots."

Alexeyev said the statement amounted to the authorities' acknowledgment of the fact that they cannot protect gays' rights. "That means that they can't provide security for gays in any location," he said.

CountryWatch: Russia

Right-wing and religious extremists have staged violent protests outside gay nightclubs in recent weeks and forced the cancellation of a cultural festival -- the actions rights groups lamented as evidence of rising homophobia.

Approximately 5-8 percent of Russia's 143-million-strong population is gay and lesbian, according to gay rights activists.