Mayor London Breed admitted to letting former Public Works chief Mohammed Nuru pay about $5,600 for expenses involving repairs to her car — a gift the mayor said she wasn’t required to disclose because the two had dated and been friends for decades.

Breed disclosed her romantic relationship with Nuru in an explosive online post Friday morning.

“Mohammed Nuru and I have been close personal friends for more than 20 years. We dated for a brief time, two decades ago, long before I ever ran for office. Nevertheless, he, and his now-adult daughters, have remained close friends for all those years,” Breed said in the post.

The gift from Nuru may have violated city ethics laws, and it was quickly picked up on by Breed’s opponents Friday.

Nuru was arrested on fraud charges, alongside San Francisco restaurateur Nick Bovis, on Jan 28. His arrest sparked a crisis in City Hall as public officials scrambled to react to the alleged government corruption scandal, and to understand how deep the self-dealing might go.

In recent days, the city’s Department of Building Inspection was visited by the FBI in connection with the federal government’s ongoing investigation into wrongdoing, along with the office of the longtime and deeply politically connected building permit consultant, Walter Wong. On Tuesday, City Attorney Dennis Herrera’s office issued subpoenas demanding a litany of financial documents showing how money might have moved between eight companies and nonprofits and government agencies, including Public Works.

“To be clear: I never asked Mohammed Nuru to do anything improper, and he never asked me to do anything improper,” Breed said in her post Friday. “I was not aware of the schemes alleged by the FBI until shortly before they became public, and when I was informed, I immediately reported the information to our City Attorney.”

While Breed’s relationship with Nuru may have ended two decades ago, the news drew sharp criticisms from San Francisco public officials and residents who have long complained about a culture of coziness among top officials that rewards personal loyalties and ignores potential wrongdoing.

In terms of the car repair, Breed wrote that Nuru, “acting as my friend,” took her personal car to a private mechanic for repairs last year. When problems with the car persisted, Nuru arranged for a rental car. The total value of both the auto work and the rental car came out to about $5,600, Breed estimated. She said she intended to sell the car and use the money from the sale to reimburse Nuru. But that has not yet occurred.

Breed claimed that state government ethics laws didn’t require her to disclose the gift because her friendship with Nuru predates their work together as top San Francisco officials. She cited state government ethics laws that exempt officials from having to report gifts from “an individual with whom the official has a long term, close personal friendship unrelated to the official’s position.” She also said she disclosed the gifts Friday “to be as transparent as possible”: she is not required to report gifts received in 2019 until April 1, 2020.

It’s unclear how that rationale meshes with San Francisco government-ethics law that forbids officials from accepting gifts from subordinates.

San Francisco District Attorney Chesa Boudin said in a statement, “I have been asked about details that emerged today regarding possible ethical violations by Mayor Breed. My office will investigate any potential criminal liability, as we take public corruption very seriously. However, the Mayor, like everyone else, is presumed innocent.”

Supervisor Hillary Ronen called for Breed’s resignation Friday, citing city ethics laws. Focusing on their romantic relationship from 20 years ago was “ridiculous,” Ronen said.

“The only relationship that matters is that she is the mayor and he was the director of Public Works — and thousands of dollars of gifts have passed between them. We can’t continue to normalize corruption in San Francisco. And we can’t call out Trump for his corruption and ignore what’s happening in our own backyard. London Breed broke the law,” Ronen said, referring to city ethics laws. “She should resign.”

Back in 2018, on the night the Board of Supervisors voted to remove Breed as interim mayor following the death of Ed Lee, Ronen delivered an impassioned speech arguing that Breed had to be ousted to prevent “tech moguls and real estate billionaires” from wielding influence on city politics through Breed.

Supervisor Matt Haney, another reliable critic of the mayor, said, “these revelations are very serious and likely illegal. You aren’t allowed to accept gifts from your subordinate. Period. This is a deep betrayal of the public trust and likely a violation of the law.”

Haney said there were “a lot of unanswered questions” about the donation. “The city attorney and likely the district attorney should launch a full investigation into the details and circumstances of this gift specifically. There’s a lot about it that doesn’t seem to add up,” he said.

The attack from Breed’s opponents is not unexpected. She said in the Friday post “that some will seek to exploit what I have shared here, to harm me politically. I, and others, may be weighed down from guilt by association as a result of this episode. But I can’t worry about that now,” stressing the need to “hold ourselves accountable to the people of San Francisco.”

In her post Friday, she added she “will not apologize for dating someone two decades ago. I will not apologize for remaining close friends with him and his family for 20 more years,” Breed said.

“But neither will I make excuses for any misdeeds. He will have to live with any consequences, and we in government must work to ensure our institutions live up to the highest levels of integrity.”

Lateefah Simon, president of the BART Board of Directors and a longtime friend of Breed, leapt to the mayor’s defense.

“We want our leaders to be forthright and that’s what she’s doing,” Simon said. “Black public officials — especially women — are always judged differently than their counterparts. She’s a black homegirl from San Francisco. Anything she’s done in her past, she knows it’ll be litigated,” she said. “I don’t feel like this mayor in particular would sacrifice the integrity of her service to the city for any staff member or any leader.”

Bevan Dufty, a BART director and San Francisco’s former homelessness czar and a former supervisor, has known Breed for decades. A rift emerged when he threw his support behind former state Sen. Mark Leno in the 2018 mayor’s race.

Still, he said, “It was heartbreaking to read her post. But I thought there was beauty in her honesty and I hope she can move on and rise above this as the investigation proceeds,” Dufty said. “I’m kind of shook-up. I had a good working relationship with Mohammed, too, and I really respected him. I was crestfallen to see someone trade their name for so little.”

Rumors of a romantic relationship between Breed and Nuru whipped around City Hall in the days following Nuru’s arrest.

The news of the relationship comes days after Nuru resigned his post as director of San Francisco Public Works.

Nuru’s and Bovis’ alleged schemes are detailed in the Justice Department’s 75-page criminal complaint that lays out information gathered from undercover officers, wiretaps and confidential sources. Nuru and Bovis, the owner of the now-closed Lefty O’Doul’s restaurants, are accused of concocting several plans, some of which were allegedly intended to steer city contracts to Bovis.

Nuru has also been accused of accepting gifts from a billionaire Chinese developer in exchange for help with a real estate deal, lying to the FBI, and receiving free and discounted building materials that he did not disclose.

The fallout from the arrests continues. In addition to the FBI investigation, the city attorney and controller’s offices are engaged in far-reaching internal probes. Supervisor Haney has said he plans to propose a ballot measure to cleave Public Works in two, forming an entirely new city agency: the Department of Street Cleaning and Sanitation, which would focus on street and sidewalk cleaning, waste management, illegal dumping and maintaining public toilets.

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa