SAN DIEGO -- Thousands of people took part Saturday in an anti-Proposition 8 demonstration in downtown San Diego that also attracted a handful of counter-protesters, one of whom was arrested.

The rally drew at least 20,000 protesters unhappy with the voter-approved same-sex marriage ban, San Diego police Sgt. Art Campa said.

"One of the pro-Prop. 8 persons was cited for trying to incite a fight," Campa said.

Police said the man was a member of the anti-illegal immigration group San Diego Minutemen, and told the San Diego Union-Tribune that he was one of several people conducting a counter-protest on Sixth Avenue at Ash Street.

The man, whose name was not released, was cited for allegedly trying to incite a fight and released.

No other arrests were made, and no other incidents were reported.

In Escondido, about 250 Prop. 8 protesters gathered in front of City Hall before marching through the city, Escondido police Lt. David Mankin said.

Toward the end of that demonstration, about seven "Yes on 8" counter- protesters showed up at City Hall, but Mankin said no conflicts were reported.

Similar rallies were held nationwide, including downtown Los Angeles, New York, Chicago, San Francisco, Atlanta and St. Louis.

Proposition 8 amended the state constitution to define marriage as a union between a man and a woman. It was approved Nov. 4 by a 52.5 to 47.5 percent margin, triggering large-scale demonstrations around Southern California.

Following the election, an attorney representing the lesbian couple whose lawsuit resulted in the California Supreme Court ruling that allowed same-sex marriage filed a writ with the high court, challenging the proposition.

The ACLU of Southern California, Lambda Legal and the National Center for Lesbian Rights also filed a petition with the court, arguing that Proposition 8 is invalid because the initiative process was improperly used to undo the California constitution's commitment to equality.

Lawyers for the city of Los Angeles and Los Angeles, San Francisco and Santa Clara counties have joined in filing a petition to invalidate Prop 8.

The Mormon church has been targeted by gay-rights activists for financially backing the proposition. The Los Angeles Mormon Temple in Westwood was closed Thursday after an envelope filled with an unidentified white powdery substance, later found to be harmless, was delivered to temple employees.

Supporters of Proposition 8 say the opposition's tactics, which include boycotting businesses that donated money to Yes on 8, have gone too far.

"These cowardly acts are intended to terrorize people," Frank Schubert, manager of the Yes on 8 campaign, said at a Friday news conference.

"They mean to frighten and to intimidate the people who supported Proposition 8 and those who have stood up for traditional marriage," he said.

"This is the very definition of terrorism and that is what is occurring in California today."