Hoping to turn their frustration and anger into action, tens of thousands of protesters against Arizona's new immigration law marched on the state Capitol Saturday and urged the nation's leaders to hear their pleas.

"We must stand together for justice, opportunity and peace," said U.S. Rep. Ed Pastor, D-Ariz., at the mid-afternoon culmination of what was a peaceful demonstration on the Capitol grounds. "What we need in the United States is not scapegoating immigrants."

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Sarahi Uribe, a representative of the National Day Laborer Organizing Network, which helped organize Saturday's event, said her California-based group participated to send a message to Washington, D.C. "We have a very clear demand that President Obama stop Senate Bill 1070," she said.

The 5-mile March Against SB 1070, which began shortly before 10a.m. at Steele Indian School Park, had no reported arrests, but the afternoon's heat took a toll, with 20 people treated for heat-related illnesses, seven of them taken to area hospitals, public-safety officials said.

An official crowd estimate was not available. Phoenix police declined to give an official tally, but officers overheard on the police scanner estimated the crowd at about 30,000. Uribe said the march drew about 100,000.

Banging drums, chanting, singing and waving American flags, the throng made its way toward the Capitol. Organizers, scattered throughout the crowds, picked up trash and provided water to the marchers.

As the temperatures climbed, several people peeled off the march to find shade. The National Weather Service said the day's high was 94 degrees.

The first of the protesters reached the Capitol about 12:30 p.m. and gathered around a stage. Mariachi bands played, and organizers called out instructions on bullhorns.

The Rev. Warren Stewart of the First Institutional Baptist Church in Phoenix directed his comments to Obama: "God put you in the White House. You are a person of color. Stand with us."

Richard Trumka, president of the AFL-CIO, spoke about the climate of fear Arizona's immigration-enforcement law has created. "Immigrants are not the cause of America's problems, and (Senate Bill) 1070 is not the answer," he said.

Eric Ruder, 40, flew in to Tucson from Chicago after learning of the protest online last week and said the influx of protesters from around the country shows the nation's interest in Arizona's law.

"The criminalization of immigrants is a scary direction that this country is heading in," Ruder said.

Protest organizers said Saturday that others from Texas, California and Washington state planned to participate. Justin Akers Chacon, 38, a college professor from San Diego, came to Phoenix Friday night with more than 100 people who slept on sleeping bags in a downtown warehouse provided by organizers.

"There was a seriousness and confidence that we're all here for the right reasons," he said. Isabel Gareja, a member of the Coalici�n de Derechos Humanos, human-rights group, said in Spanish: "We're going to resist. Resistance is the word of the day."

Arizona's immigration law, signed by Gov. Jan Brewer April 23, is set to take effect July 29. The law makes it a state crime to be in the country illegally. It states that an officer engaged in a lawful stop, detention or arrest shall, when practicable, ask about a person's legal status when reasonable suspicion exists that the person is in the U.S. illegally.

The law has sparked protests nationwide, boycotts of Arizona from other cities and groups and spurred a number of lawsuits challenging its legality. The Department of Justice also is considering whether to challenge it.

Despite the rising opposition, polls have consistently indicated that the majority of Arizonans support the measure. A rally in support of the law � Stand with Arizona � was held Saturday evening at Tempe Diablo Stadium, drawing more than 5,000.

Derek Dauma, 37, who lives near Steele Indian School Park, only had to stand along Third Street to share his view of the law. He held a sign that read "Respect U.S. laws."

"The system in general is broken. Employers are not being punished for hiring illegal immigrants," Dauma said. "People coming here illegally is unfair to the people who've waited years and years."

For some protesters, the Arizona law hits particularly close to home.

Marlene Vazquez,18, said she came to the country illegally 16 years ago with her family. They stood together at the park Saturday morning concerned about the impact the law could have on their lives.

Like many opponents of the bill, Vazquez is concerned that it will lead to police targeting Hispanic-looking residents in an effort to root out illegal immigrants.

"There's no way that they're not going to racially profile," she said. "How does someone look illegal?"

Reporters Connie Cone Sexton, JJ Hensley, Dustin Gardiner, Allison Hurtado, Brittany Williams, Colin Lecher, Jessica Testa and Ofelia Madrid contributed to this article.