The Rev. Al Sharpton kicked off his National Action Network convention Wednesday with praise from New York City Mayor Bill de Blasio, who called the civil rights leader a "blessing."

"To borrow a phrase from our youth, reverend, 'He's the real thing,'" de Blasio said.

The four-day convention in Manhattan -- set to feature a keynote address Friday by President Barack Obama and to be attended by Gov. Andrew M. Cuomo, among other officials -- began amid news reports detailing Sharpton's work as an FBI informant in the 1980s, when he recorded conversations with Mafia figures.

The civil rights leader this week insisted he is not a "rat" but rather a "cat" who catches rats. He said he did the right thing and would do it again if his life was threatened.

De Blasio Wednesday made no mention of Sharpton's work against the mob and instead commended his career arc.

"I've had the pleasure of watching Rev's work over decades now," de Blasio said. "When we find someone who actually stays the course -- and in fact, becomes better, stronger, clearer at the work with every passing year -- that's a blessing."

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Sharpton in turn said de Blasio's fledgling administration brings the promise of a different city.

De Blasio called for voters rights around the country, touted paid sick leave and denounced racial profiling in policing, pointing to Sharpton's organizing of a march two years ago against stop-and-frisk abuses.

"Crime remains low, but social justice is increasing," de Blasio said of policing.

The mayor is to deliver a speech Thursday at Cooper Union to mark his administration's 100-day mark.

U.S. Attorney General Eric Holder, the first African-American to hold that position, spoke afterward at the convention about "equality under the law."

Racial profiling is wrong and counterproductive, he said, adding that he has personally experienced profiling.

"Compliance with the law begins not with the fear of arrest or even incarceration but with respect for an institution that guides our democracy," Holder said. "Protecting public safety and protecting our civil rights are not mutually exclusive. "