Portside

At a star-studded gathering of mostly black performers to honor Dr. King, organized at Riverside Church in Harlem, mentions of the Academy Awards were kept in check, even by those whose films and performances were ignored.

Neither the event’s host, Ryan Coogler, the director of “Creed,” nor the film’s stars, Michael B. Jordan, who read a Fred Hampton speech before a rapt crowd, and Tessa Thompson, who read one by Angela Davis, alluded to the complaints surrounding the nominations. (The only Oscar nomination for “Creed” went to Sylvester Stallone, for his performance as a supporting actor.

Chris Rock, the comedian scheduled to host the awards, also kept on message after taking to the church’s stage following Mr. Jordan, reciting “My Dungeon Shook” by James Baldwin.

Earlier in the day, Mr. Lee had announced on Instagram and Ms. Pinkett Smith through a video their intentions not to attend the awards because, for the second year in a row, none of the actors nominated are black. But they did not call on Mr. Rock to do the same.

Referring to himself and his wife, Mr. Lee wrote, “We cannot support it and mean no disrespect to my friends,” naming Mr. Rock; one of the producers, Reginald Hudlin; and Cheryl Boone Isaacs, the Academy of Motion Picture Arts and Sciences president. All three are black.

In a video released on Monday, Ms. Pinkett Smith said of Mr. Rock, “I can’t think of a better man to do the job at hand this year than you my friend, and good luck.”

Ms. Pinkett Smith had already taken aim at the Academy on Saturday, asking on Facebook and Twitter, “Should people of color refrain from participating all together?” She added, “People can only treat us in the way in which we allow.”

She answered her own question on Monday, saying, in the video, “We can no longer beg for the love, acknowledgment or respect of any group.” Her husband, Will Smith, was a best actor contender for his lead role in “Concussion” but received no nomination.

Mr. Lee’s boycott is especially fraught for the Academy because, though he received an honorary Oscar in November; his latest film, “Chi-Raq,” earned no nominations. Saying he was tired of being asked for his opinion about all-white or majority-white Oscar races year after year, he also urged the news media to “ask all the white nominees and studio heads how they feel about another all-white ballot.”

On Monday evening, the Academy’s president, Ms. Isaacs, issued a statement saying she was “both heartbroken and frustrated about the lack of inclusion” in this year’s nominees and adding, “This is a difficult but important conversation, and it’s time for big changes.”

The Academy’s diversity push in recent years had not brought change fast enough, Ms. Isaacs wrote, and she promised a review of its recruitment efforts.

Having only white nominees in acting categories for two years straight is an aberration in recent Oscar history; the last time no black actors received nominations for two consecutive years was in 1997 and 1998.

Yet the homogeneity of Hollywood has recently come under increased scrutiny. The American Civil Liberties Union called for a government investigation into potentially discriminatory hiring practices last May. And the Directors Guild of America released a study in December showing that 82 percent of movies from 2013 and 2014 were directed by white men.

Meanwhile, in London, the actor Idris Elba — who was shut out of Oscar contention despite being a heavy favorite for his performance in “Beasts of No Nation” — denounced the lack of diversity in British television to lawmakers there.

Performers and speakers at the Harlem event, which is new this year and organized by Blackout for Human Rights and the Campaign for Black Male Achievement, included J. Cole, Lin-Manuel Miranda, Octavia Spencer, India Arie and Harry Belafonte, who read Patrice Lumumba’s Independence Day speech. The crowd murmured and cheered, often rising to their feet as rousing historic words were read.

Mr. Belafonte was one of the few people who ventured off script, reminiscing about meeting Dr. King when they were both in their 20s.

“If we can fix America,” Mr. Belafonte said, “we will indeed have fixed most of the ills of the world.”