A top immigration official said Wednesday that about 800 people living illegally in Northern California were able to avoid arrest because of a weekend warning that Oakland Mayor Libby Schaaf put on Twitter.

“What she did is no better than a gang lookout yelling ‘police’ when a police cruiser comes in the neighborhood, except she did it to a whole community,” Thomas Homan, the Immigration and Customs Enforcement acting chief, told “Fox and Friends.”

The mayor warned residents over the weekend of large-scale, impending raids by immigration agents in the San Francisco Bay Area, escalating tensions between California officials and the Trump administration.

Homan said the Justice Department is looking into whether Schaaf obstructed justice and said her actions allowed immigrants who have committed crimes to remain in Oakland, making the community less safe.

“I just can’t believe it happened,” he said.

Federal immigration agents arrested more than 150 people in California in the days after Schaaf’s warning of the raids, the agency announced Tuesday.

Agents made the arrests in a three-day sweep starting Sunday that covered cities from Sacramento in the north to Stockton in California’s Central Valley agricultural heartland. About half of those arrested for being in the country illegally had criminal convictions, the agency said.

Schaaf, a Democrat who is running for re-election this year, warned residents on Twitter Saturday night that “credible sources” told her a sweep was imminent, calling it her “duty and moral obligation” to warn families.

California lawmakers from Gov. Jerry Brown, also a Democrat, down to local mayors have resisted a Trump administration immigration crackdown that they contend is arbitrarily hauling in otherwise law-abiding people and splitting up families that include U.S.-born children.

In a statement Tuesday, Homan suggested the sweep targeted so-called “sanctuary cities” that limit cooperation between ICE and local law enforcement.

“Sanctuary jurisdictions like San Francisco and Oakland shield dangerous criminal aliens from federal law enforcement at the expense of public safety,” Homan said. “Because these jurisdictions prevent ICE from arresting criminal aliens in the secure confines of a jail, they also force ICE officers to make more arrests out in the community, which poses increased risks for law enforcement and the public.”

Defenders of sanctuary city practices say they improve public safety by promoting trust among law enforcement and immigrant communities and reserving scarce police resources for other, more urgent crime-fighting needs.

ICE said those arrested included several people with convictions for crimes such as assault with a deadly weapon, including a man who had been previously deported to Mexico eight times.

Schaaf said in a statement Tuesday night that her earlier warning “was meant to give all residents time to learn their rights and know their legal options.”

“I do not regret sharing this information,” Schaaf added. “It is Oakland’s legal right to be a sanctuary city and we have not broken any laws. We believe our community is safer when families stay together.”

The immigration sweep was the second in California since a statewide sanctuary law took effect last month. Agents have arrested more than 200 people earlier this month in the Los Angeles area.

(AP)