SANFORD, Florida (Reuters) - U.S. President Barack Obama called for calm on Sunday after the acquittal of George Zimmerman in the shooting death of black teenager Trayvon Martin, as hundreds of civil rights demonstrators turned out at rallies to condemn racial profiling.

Zimmerman, cleared late Saturday by a Florida jury of six women in the shooting death of the unarmed Martin, still faces public outrage, a possible civil suit and demands for a federal investigation.

In Washington, the U.S. Justice Department said it was evaluating whether it has enough evidence to support prosecution of Zimmerman in federal court after his acquittal in Florida.

Civil rights activists have been pressuring the Obama administration to bring civil rights charges in federal court.

Critics contend Zimmerman wrongly suspected 17-year-old Martin of being a criminal because he was black, making it a civil rights issue. At a rally in New York’s Union Square, more than 200 protesters turned out Sunday, chanting “No justice, no peace.” Some held signs calling for “Justice for Trayvon, Jail for Zimmerman.”

Similar rallies were held or expected to start later in other cities including Boston, San Francisco, San Diego and Sacramento.

Obama, who once said, “If I had a son, he’d look like Trayvon,” called for a peaceful response to a case that polarized the U.S. public from the beginning, raising issues of racial profiling and gun control.

“We are a nation of laws and a jury has spoken,” the first black U.S. president said in a statement. “I now ask every American to respect the call for calm reflection from two parents who lost their young son.”

The jurors who deliberated for 16 hours over two days found Zimmerman not guilty of second-degree murder and manslaughter. If found guilty of the most serious charge, Zimmerman could have faced life in prison.

Zimmerman’s lawyers argued he acted in self-defense the night of February 26, 2012, when he and Martin met inside a gated community in the central Florida town of Sanford. They accuse civil rights advocates of wrongly injecting the issue of race.

“It was such a shame. The whole case nearly destroyed George from Day One ... . That they put a racism spin on this prosecution just hurt him very deeply,” said John Donnelly, a close friend of Zimmerman who testified in the trial.

In Sanford at the largely black Allen Chapel A.M.E. Church, pastor Valarie Houston dedicated a Sunday morning prayer service to Martin.

“I am hurt. I am sad. I am disappointed and my heart is overwhelmed with pains,” Houston said. “I thought in my heart that justice would be served.”

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Civil rights leaders including Jesse Jackson, Al Sharpton and Benjamin Jealous, president of the National Association for the Advancement of Colored People (NAACP), urged the Justice Department to pursue federal civil rights charges against Zimmerman.

Jealous said Martin’s family may bring a civil suit against Zimmerman but said federal criminal charges should be filed because evidence suggests race was a factor in the case.

A Justice Department spokesperson said in a statement on Sunday it would determine whether “the evidence reveals a prosecutable violation of any of the limited federal criminal civil rights statutes within our jurisdiction.”

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‘WE DON’T GET JUSTICE’

The jurors, who were sequestered during the three weeks of testimony and remained anonymous by court order, have declined to speak with reporters since handing down the verdict in one of the highest-profile trials of the year.

Zimmerman, who showed little reaction when the decision was read, was unshackled from a monitoring device he had been wearing while on bail. He previously only left home in a disguise and body armor, his lawyer said.

His brother said he would remain out of public view for some time, but friends said the former neighborhood watch volunteer had recently spoken about the possibility of entering law school.

The tense drama that climaxed with the verdict had been building for more than a year, since police initially declined to arrest Zimmerman for shooting Martin, whose gray hooded sweatshirt has become a symbol of injustice for many.

Zimmerman, 29, who is white and Hispanic, spotted Martin from his car and called police, believing Martin to be suspicious. The teenager, who was staying in the neighborhood at the home of his father’s fiancee, was walking back from a convenience store where he had bought candy and a soft drink.

Minutes later, after Zimmerman got out of his car, the two engaged in a fight that left Zimmerman with a bloody nose and head injuries. The encounter ended when Zimmerman shot Martin once through the heart with a 9mm pistol.

Prosecutors had to prove that Zimmerman committed a crime in pursuing and killing Martin and that he did not act in self-defense, a bar they failed to clear with jurors.

The acquittal will weaken any wrongful death civil lawsuit that Martin’s family might bring. Zimmerman’s lead defense lawyer, Mark O’Mara, predicted Zimmerman would seek and win immunity from a civil suit.

Around Sanford, some residents expressed relief at the verdict, while others said they failed to see how Zimmerman could have been acquitted.

“You said he’s not guilty, but why would you say he’s not guilty?” said 28-year-old Robyn Miller. “It’s crazy.”

At rallies in Boston and New York, several hundred demonstrators expressed a similar sense of frustration. “I feel we don’t get justice when it’s needed,” said Kabrina Oliver, 18, a Boston high school student.