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Chris Rock spoke on Monday at the Riverside Church in New York City. CreditJulieta Cervantes for The New York Times 
The outcry over the nomination of 20 white actors, and no black ones, for the Academy Awards gained momentum on Monday — Martin Luther King’s Birthday — as the director Spike Lee and the actress Jada Pinkett Smith announced they would not be attending the ceremony on Feb. 28.
But 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 by memory “My Dungeon Shook” by James Baldwin.
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Spike Lee at the premiere of his latest film, “Chi-Raq,” at the Ziegfeld Theater in New York.CreditCharles Sykes/Invision, via Associated Press 
Mr. Rock made only one joke.
“I don’t really appreciate having to follow the heartthrob,” he said of Mr. Jordan. “But I will try my best.”
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, who is 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 whether people of color should boycott the ceremony. “People can only treat us in the way in which we allow,” she wrote.
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Jada Pinkett Smith at the Golden Globes this month.CreditValerie Macon/Agence France-Presse — Getty Images 
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.”
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 in its first 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 twenties.
“If we can fix America,” Mr. Belafonte said, “We will indeed have fixed most of the ills of the world.”