Director Spike Lee, leading the call for an Oscars boycott, called on Tuesday for affirmative action in Hollywood to address racial disparity while civil rights leader Al Sharpton urged Americans to "tune out" the Academy Awards ceremony next month.

George Clooney and British actor David Oyelowo joined those calling for changes in the movie industry and at the Academy of Motion Picture Arts and Sciences, whose members nominated no actors of colour for the 2016 Oscars for a second straight year.

"If you think back 10 years ago, the Academy was doing a better job. Think about how many more African Americans were nominated. I would also make the argument, I don't think it's a problem of who you're picking as much as it is: How many options are available to minorities in film, particularly in quality films?", Clooney told Hollywood trade paper Variety.

A day after calling for an Oscars boycott, Lee, who has an honorary Oscar, said Hollywood had fallen behind music and sports in reflecting racial diversity.

Lee cited a National Football League rule that requires teams to interview minority candidates for head coaching and senior executive jobs.

"Why Can't Hollywood Do The Same?" the "Chi-Raq" director wrote on his Instagram page.

Sharpton said he planned to meet with other civil rights groups to launch a "serious campaign for people to tune out the Oscars."

Documentary-maker Moore said he would join the boycott, along with Jada Pinkett-Smith, the wife of snubbed "Concussion" star Will Smith. But as of Tuesday, no other major stars had said they would boycott the Feb. 28 ceremony.

READ: Spike Lee, Jada Pinkett Smith to boycott Oscars

Cheryl Boone Isaccs, the African-American president of the Academy, on Monday pledged big but unspecific changes and a review of the way members are recruited.

Membership of the Academy is by recommendation of two other members, or is automatically awarded to Oscar nominees. The list of the 6,000 or so Academy members has never been disclosed although a 2012 Los Angeles Times study found that its members were nearly 94 percent white and 77 percent male.

In recent years, the Academy has begun publishing lists of new members. They include Chris Rock - the 2016 Oscars host - , Oscar winner Lupita Nyong'o, "Selma" director Ava DuVernay, comedian Kevin Hart and Steve McQueen, the black British director of 2014 Oscar-winning movie "12 Years a Slave."

Oyelowo, who was widely perceived to have been snubbed last year for his performance as Martin Luther King Jr. in "Selma," said the Academy needs to move fast to fix the problem.

"This institution doesn't reflect its president ... I am an Academy member and it doesn't reflect me, and it doesn't reflect this nation," Oyelowo was quoted by TheWrap.com as saying in a Hollywood gala speech on Monday.

Lee's call for a boycott has not been universally supported.

John Singleton, Oscar-nominated for directing the 1991 film "Boyz n the Hood", said nominations for the industry's most prestigious awards are a lottery.

"People even complain even when we have a lot of nominations. It is what it is. I've been in the game for 25 years. You never know - it's the luck of the draw for you," Singleton was quoted as telling Variety.

Janet Hubert who appeared in 1990s TV comedy series "The Fresh Prince of Bel-Air," accused the Smiths of hypocrisy, saying they have made "millions and millions of dollars from the very people that you're talking about boycotting just because you didn't get a nomination."