Following attacks and arrests of protesters at the demonstration, Pink News quoted Peter Tatchell as saying: "The Moscow police gave right-wing extremists a more or less free hand to attack Gay Pride marchers. Despite many of us being battered left, right and centre, the police only arrested a handful of the assailants."
Demonstrators including European lawmakers, senior foreign human rights officials and celebrities, had gathered to submit a letter, signed by around 50 members of the European Parliament, protesting against the Moscow mayor's ban of a gay pride parade.
Tatchell told the news service: "I urge people to protest to the Russian Ambassador and to ask their local MPs to send a letter of protest to the Russian embassy."
Activists had planned to hold a gay pride march on central Moscow's Tverskaya Street, but were denied permission for the second year running by the city's conservative Mayor Yury Luzhkov, who has branded such events as "satanic." Protesters, numbering around 100, gathered outside the capital's City Hall to submit the letter.
Among those arrested were Marco Cappato, an Italian member of the EU parliament, and German MEP Volker Beck. The German politician told agencies that he and other protestors had been beaten by police, and denied that the gathering had been a demonstration, saying it was merely an attempt to submit a letter of protest.
The incident, at which riot police forcefully dispersed protesters and arrested dozens, threatens to fuel Western criticisms over the country's record on human rights and democracy, in particular the right to hold protests. The chairwoman of Germany's Green party, Claudia Roth, has called on Chancellor Angela Merkel to raise the issue with President Vladimir Putin at the Group of Eight summit in June.
Russia is a member of the Council of Europe, and a signatory to the European Convention of Human Rights, which obliges the state to allow demonstrations to be held.
Roth told UK newspaper The Guardian: "It has been shown once again today that human rights are systematically abused in Putin's Russia."
Russia's president, despite his high popularity rating within the country, is widely criticized in the West for stifling democracy. At a summit with the European Union near Samara 10 days ago, Putin was challenged by EU leaders over authorities' refusal to allow demonstrators to travel to the summit.
The president said: "I think such actions [as opposition protests] must be organized within the law, and should not interfere with other people's everyday lives."
The Russian leader, who has repeatedly accused the West of interfering in his country's domestic affairs, also hit back at the EU, saying: "Police and law enforcement agencies in Europe also take preventive measures."
At a Kremlin news conference in February the president was confronted over the Moscow mayor's refusal to allow gay and lesbian parades. He avoided a direct answer, but signaled his support for Yury Luzhkov, and joked that issue of sexual minorities was linked to the demographic problem in the country.
The German and British foreign ministries, both approached by politicians to condemn Moscow authorities' handling of Sunday's demonstration, have so far declined to give official comment.
Homosexuality was legalized in Russia in 2003, but discrimination against gays and lesbians remains widespread. The hostile crowd at Sunday's demonstration included people carrying crosses and wearing Orthodox Church clothing, along with ultra-nationalists.
Peter Tatchell told the gay news service that the gay pride parade ban was "one aspect of a much wider attack on civil society and human rights."