(AP) -- Oprah Winfrey and fellow actors from the movie "Selma" marched with hundreds in a tribute to Martin Luther King Jr., one of many events around the nation ushering in Monday's federal holiday for the slain civil rights leader.

Remembrances of the King legacy come amid somber reflection by many on incidents in which unarmed black men were killed by police in recent months, spurring protests and heightening tensions in the U.S. In Ferguson, Mo., where one fatal shooting caused weeks of violent protests, leaders urged reforms to the criminal justice system in the name of equality.

"We need to be outraged when local law enforcement and the justice system repeatedly allow young, unarmed black men to encounter police and then wind up dead with no consequences," said U.S. Rep. William Clay, a St. Louis Democrat. "Not just in Ferguson, but over and over again across this country."

The King holiday, meanwhile, was being met with activities nationwide, including plans for a wreath-laying in Maryland, a tribute breakfast in Boston and volunteer service activities by churches and community groups in Illinois. In South Carolina, civil rights leaders readied for their biggest rally of the year.

Winfrey helped lead a march by hundreds on Sunday with "Selma" director Ava DuVernay and actor David Oyelowo, who played King in the movie.

"Selma" chronicled turbulent events leading up to the historic march from Selma to Montgomery, Alabama, and the subsequent passage of the 1965 Voting Rights Act. Winfrey played activist Annie Lee Cooper in the movie, which was nominated for two Oscars, in categories of best picture and best original song.

A producer on the film, Winfrey praised the 1965 marchers for their courage in meeting fierce opposition on the Edmund Pettus Bridge in Selma -- scene of Sunday's remembrance march.

"Look at what they were able to do with so little, and look at how we now have so much," Winfrey said. "If they could do that, imagine what now can be accomplished with the opportunity through social media and connection, the opportunity through understanding that absolutely we are more alike than we are different."

White officers used clubs and tear gas on March 7, 1965 -- "Bloody Sunday" -- to rout marchers intent on walking some 50 miles to Montgomery, the Alabama capital, to seek the right for blacks to register to vote. King led a new march later that month that reached Montgomery, with the crowd swelling to 25,000.

Elsewhere, King's legacy was being celebrated with days of events in Atlanta, especially at the church he once pastored. The current pastor of Ebenezer Baptist Church, the Rev. Raphael Warnock, said the annual King holiday is a time when "all of God's children are busy spreading the message of freedom and justice."

On Monday, Oyelowo planned to deliver a holiday tribute to King at Ebenezer Baptist Church in Atlanta, where church members over the weekend sang the civil rights anthem, "We Shall Overcome."

Calls for unity were heard during the events surrounding the King holiday.

During Sunday's march in Selma, Common and John Legend performed their Oscar-nominated song "Glory" from the film as marchers crested the top of the bridge as the sun set. Common had a part in the movie and said that song sought to show the link between the struggle of the past and today's injustices.

"We are the ones that can change the world," Common said afterward. "It is up to us, and it takes all us -- black, white, Latino, Asian, native-American, whatever nationality or religious background. There is a certain togetherness that we've got to have."

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AP writers Alan Schere Zagier in Ferguson, Missouri, and AP Radio Religion Editor Steve Coleman in Washington, D.C., contributed to this report.