NEW YORK (Reuters) - Tributes to civil rights leader Martin Luther King Jr. were held nationwide on Monday as protests over the treatment of minorities by law enforcement rolled on across the country.

Observers of Martin Luther King Jr. Day have this year linked the federal holiday to a rallying cry in recent months during demonstrations over police brutality: "Black lives matter."

King's 1960s dream of racial equality was being viewed through a lens focused on the recent deaths of unarmed black men after confrontations with police, including Eric Garner, who died in July after being put in a choke hold in New York City, and Michael Brown, shot in Ferguson, Missouri, in August.

More than 1,800 people pressed into a King commemoration service at the Ebenezer Baptist Church in Atlanta, where King once preached, some holding signs with his famous quote "I am a man," others with placards reading "I can't breathe" in Garner's memory and "Hands up! Don't shoot!" to honor Brown.

"We look at the yellow crime scene tape that's wrapped around America now and we know that we have a lot of work still to do," Gwendoyln Boyd, president of Alabama State University, told the crowd that responded with an earsplitting "Amen!"

MLK Called 'Disruptive'

About 400 protesters blocked traffic in New York City as they walked about 60 blocks from Harlem to near the United Nations, chanting "Black lives matter!" as King's speeches blared from loudspeakers.

"This march is about reclaiming Martin Luther King. He was a radical organizer - he's been arrested, he believed in non-violence, but he was also disruptive," said Linda Sarsour, spokeswoman for the Justice League NYC, which organized the #Dream4Justice March.

Hours before an evening vigil on the Staten Island street where Garner died, his family placed wreaths on the Brooklyn street where two uniformed officers were ambushed in December by a gunman claiming to avenge the deaths of Garner and Brown.

"This holiday should also represent that we are unequivocally against the shedding of innocent blood," said the Rev. Al Sharpton, who accompanied Garner's widow, mother and children as they laid down the arrangements of blue hyacinths and white roses.

Protests in other U.S. cities included a pre-dawn rally in Oakland, California on Monday, about 40 demonstrators converged on the home of Mayor Libby Schaaf, calling for harsher punishment of police who use violence against civilians.

They chalked outlines of bodies on the tree-lined street, played recordings of King's speeches and projected an image of the slain civil rights leader with the words "Black lives matter," on the mayor's garage door.

President Barack Obama, the nation's first African-American president, took a more traditional approach to honoring King on Monday, spending the day working with his family and other children on a literacy project at a Washington charity.

Obama has shied away from race-related activism, but after a grand jury failed to indict a white officer in Brown's death, he spoke out against what he called the "deep distrust" between law enforcement and black Americans, vowing to use his last two years in office to improve community policing and trust between the groups.