An illegal immigrant gang member from El Salvador was allowed to walk free from Rikers Island under Mayor Bill de Blasio’s “Sanctuary City” law — in defiance of a federal petition to hold him for deportation, officials said Tuesday.

“This man is by his own admission a member of a violent street gang and he was released back into the community,” said Thomas Decker, field office director for the US Immigration and Customs Enforcement unit in New York. “Honoring a detainer request is not about politics, it is about keeping New York citizens safe.”

Estivan Rafael Marques Velasquez, an admitted member of the notorious MS-13 gang, was released from Rikers Island on Feb. 16 after serving time for disorderly conduct.

ICE officials had requested last May that Velasquez — who was ordered removed by an immigration judge in November 2015 — be turned over to them when he was done serving his sentence, but no one at ICE was alerted to his release.

They were forced to send their own agents to find him, and they were able to track him down the same day in Queens.

“He has been processed and is now in … detention pending removal,” ICE said in a statement Tuesday.

The 19-year-old Salvadoran national has a criminal history in the United States that includes second-degree reckless endangerment, fourth-degree criminal possession of a weapon and disorderly conduct, federal officials said.

But Velasquez’s convictions are not on the city’s list of roughly 170 offenses that are deemed serious or violent under de Blasio’s 2014 Sanctuary City law.

City officials do not notify federal agents about the release of illegal immigrants convicted of minor crimes.

“The detainee was released after he pled guilty and served his time to an offense that does not qualify as a violent or serious felony under the city’s local laws‎, and his gang affiliation was not supported by evidence that meets even minimal constitutional standards,” City Hall spokesperson Rosemary Boeglin said.

“When ICE presents evidence to our city that an individual in our custody has been convicted of a violent or serious offense — one that threatens the public’s safety — we will fully cooperate.”

State Sen. Martin Golden (R-Brooklyn) said he was “amazed” that an “admitted gang member” wasn’t turned over to federal authorities.

“When ICE has a detainer on an illegal immigrant with a criminal record, they should be turned over to the federal government — no questions asked,” he said. “The lowlives who are committing crimes — get them out of here.”

Decker said the city’s policy is “creating a potentially unsafe environment for its residents.”

“ICE remains steadfast in solidifying its relationship with local law enforcement in the interest of public safety and national security,” he added.

A spokesperson for ICE could not offer additional details on Velasquez’s criminal history, including when and where he’s been arrested.

Additional reporting by Danika Fears