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.

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.