U.S. civil rights activists vowed on Saturday that, during the presidency of Donald Trump, they will defend hard-fought gains in voting rights and criminal justice, as they kicked off a week of protests ahead of the Republican's inauguration.

About 2,000 mostly black protesters ignored steady rain to march and rally near Washington's Martin Luther King Jr. Memorial, as speakers urged them to fight for minority rights and U.S. President Barack Obama's signature health-care law, which Trump has vowed to dismantle. 

The Rev. Al Sharpton, the rally's organizer, said Democrats in Congress needed to be sent a simple message: "Get some backbone."

"We march in the driving rain because we want the nation to understand that what has been fought for and gained, that you're going to need more than one election to turn it around," he said.

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U.S. civil rights activists in Washington vowed on Saturday to defend hard-fought gains in voting rights and criminal justice during the presidency of Donald Trump. (Aaron P. Bernstein/Reuters)

Crowds also gathered at rallies in Washington, Chicago, Los Angeles and San Jose, Calif.

Trump, a New York real estate developer, won with a populist platform that included promises to build a wall along the Mexican border, restrict immigration from Muslim countries and dismantle Obama's signature healthcare law.

His choice of Senator Jeff Sessions, an Alabama Republican, to become attorney general has raised concern among many on the left that Trump could weaken voting rights for minorities and roll back criminal justice reforms.

'We will march until hell freezes over, and when it does, we will march on the ice.' - Cornell William Brooks, NAACP

"We will march until hell freezes over, and when it does, we will march on the ice," said Cornell William Brooks, president and chief executive of the National Association for the Advancement of Colored People.

The rally, which drew fewer attendees than organizers had expected, also included the Hispanic group La Raza, politicians, relatives of African-Americans slain by police, the National Urban League, Planned Parenthood and the Human Rights Campaign, an advocacy group for lesbian, gay, bisexual and transgender civil rights.

Immigration Rallies Trump

Immigrant rights advocates demonstrate against U.S. president-elect Donald Trump's immigration policies during a rally at Metropolitan AME Church in Washington. (Jose Luis Magana/Associated Press)

A standing-room-only crowd packed into a historic African-American church in downtown Washington. The line to enter Metropolitan AME Church in Washington stretched nearly a city block.

People attending included immigrants who lack permission to be in the country and their relatives and supporters. Also present were elected officials, clergy and representatives of labour and women's groups.

Undocumented immigrants speak out 

Participants carried signs with messages including "Resist Trump's Hate" and "Tu, Yo, Todos Somos America," which translates to "You, me, we all are America."

"I stand here because I have nothing to apologize for. I am not ashamed of my status because it is a constant reminder to myself that I have something to fight for," said Max Kim, 19, who was brought to the U.S. from South Korea when he was 6 and lacks legal permission to stay in the country.

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U.S. Representative John Lewis, seeing here hugging President Barack Obama during an event marking the 50th Anniversary of the Selma, Ala., civil rights marches, will not attend Trump's inauguration. (Saul Loeb/AFP/Getty Images)

The church crowd urged Trump and the Republican-controlled Congress not to undo the Deferred Action for Childhood Arrivals program, aimed at helping people like Kim who were brought to the country as children.

Trump blasts civil rights legend

The rallies came hours after Trump blasted U.S. Representative John Lewis after the Georgia Democrat and civil rights campaigner said Russia's alleged hacking aimed at helping Trump put his legitimacy into question.

President-elect push back2:51

Trump replied on Twitter that Lewis should focus instead on his Atlanta district. "All talk, talk, talk - no action or results! Sad!," he wrote.

Lewis, among the most revered leaders of the civil rights movement, suffered a skull fracture during the march in Selma, Ala., more than a half-century ago and has devoted his life to promoting equal rights for African-Americans.

About 30 groups, almost all of them anti-Trump, have gotten permits to protest before, during and after the inauguration. Thousands of demonstrators have vowed to shut down the inauguration. Washington police and the U.S. Secret Service plan to have some 3,000 extra officers and an additional 5,000 National Guard troops on hand for security.

By far the biggest event will be the Women's March on Washington the day after the inauguration, which organizers say could draw 200,000 people.

Civil rights activists take to the streets ahead of Trump's inauguration2:21

With files from The Associated Press