SELMA, Ala. — 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 today’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.

“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 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” chronicles turbulent events leading up to the historic march from Selma to Montgomery, Ala., and the subsequent passage of the 1965 Voting Rights Act. Winfrey plays activist Annie Lee Cooper in the movie, which was nominated for two Oscars.

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.