Several dozen assailants attacked a gay pride march in Kyiv on June 6, throwing flares and wounding several police officers.
The Ukrainian Interior Ministry says five police officers were injured -- one seriously -- in the clashes.
The parade of the LGBT (lesbian, gay, bisexual, and transgender) community, named Equality March and numbering about 300 people, was guarded by some 2,000 police officers.
Kyiv Mayor Vitali Klitschko said the assault on gay pride marchers and police in the Ukrainian capital was "unacceptable" and that those responsible would be punished.
Klitschko said he had warned antigay activists not to "fan hostility" or "create a standoff."
Despite the heavy police presence, the march came under attack and 25-30 "hooligans" were arrested, parliament member Serhiy Leshchenko said on Twitter.
Leshchenko said police had prevented any direct clashes between participants in the march and the attackers.
Before the march, the far-right organization Right Sector -- which fields a battalion of soldiers to fight against Russia in eastern Ukraine -- called gay people "perverts" who "need to be cured" and promised to "prevent this sodomist gathering."
Annual gay pride marches are often disturbed by extremists and ultraconservatives.
Ukrainian authorities have increased their support for LGBT rights since a new pro-European government came to power after last year's "Maidan" street protests, but critics say homophobic attitudes remain widespread.