Mayor Bill de Blasio should be “ashamed” of his involvement with indicted restaurateur Harendra Singh, GOP mayoral challenger Nicole Malliotakis said Thursday.

Singh, a longtime donor to de Blasio’s campaigns, held fundraisers for the mayor and was appointed to his inaugural committee. Top officials in de Blasio’s administration intervened in Singh’s dispute with the city over more than $1 million in rent and other fees Singh owed for his now-closed Water’s Edge restaurant in Queens, which is on city-owned land. The matter long had been handled by lower-level personnel.

Standing outside the shuttered Water’s Edge in Queens, Malliotakis said de Blasio “all along had been rewarding him simply because he was a donor and that is why this mayor is a failure.”

Malliotakis, a state assemblywoman from Staten Island, called de Blasio’s relationship with Singh “a symbol of all that is wrong in Bill de Blasio’s New York.”

De Blasio campaign spokesman Dan Levitan denied the assertions but did not answer a follow-up seeking specifics about what was untrue.

“This is another pathetic attack from a candidate who is desperate to avoid talking about her votes against raising the minimum wage, her ties to the right-wing billionaires who brought us Donald Trump, or her support for turning the NYPD into Trump’s deportation force,” Levitan said.

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The “billionaires” reference was to Robert Mercer, co-CEO of the East Setauket hedge fund Renaissance Technologies, and his daughter, Rebekah, who have contributed the legal maximum of $4,950 each to Malliotakis’ campaign.

Singh was arrested and charged in 2015 by the FBI for bribing a now-former Oyster Bay Town official, tax fraud and lying to federal agents. He’s also at the center of a case involving Nassau County Executive Edward Mangano, who pleaded not guilty last fall to federal charges that he got bribes and kickbacks from Singh in exchange for county work.

The Manhattan U.S. attorney’s office in March dropped an investigation into de Blasio’s campaign-finance tactics, including those with Singh, finding insufficient evidence to charge anyone. But the office said de Blasio’s team fielded requests from favor-seekers “after which the mayor made or directed inquires to relevant city agencies on behalf of these donors.”

Malliotakis said she “might” rehire Ricardo Morales, a city official who said he was fired by the de Blasio administration because he voiced concern that Singh was getting special treatment as a donor.

Morales, a former deputy commissioner at the city’s administrative services agency, has filed a notice that he plans to sue the city for at least $5 million. He says he was “unlawfully” let go.