Federal officials said Tuesday they arrested more than 150 undocumented immigrants in a Northern California sweep aimed at countering local sanctuary laws, while suggesting Oakland Mayor Libby Schaaf’s decision to alert the public to the secret operation may have allowed some targets to elude capture.

Since Sunday, U.S. Immigration and Customs Enforcement officers have fanned out from the Central Valley to the far northern reaches of the state, knocking on doors, detaining people and prompting alarm from community activists and some Democratic politicians who oppose President Trump’s immigration crackdown.

Agency officials, who had remained silent about the operation for three days, said in a written statement that they arrested people in cities including San Francisco, Bay Point, Sacramento and Stockton, and that half of those arrested had criminal convictions, including for violent crimes.

The operation was named Keep Safe. Officials did not say whether the first letters of the operation were intended as a reference to Kate Steinle, the San Francisco woman shot dead on a bay pier in July 2015 by a homeless undocumented immigrant. ICE also did not say whether the sweep was over.

“Sanctuary jurisdictions like San Francisco and Oakland shield dangerous criminal aliens from federal law enforcement at the expense of public safety,” said Thomas Homan, the acting director of ICE. “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.”

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Homan slammed Schaaf, who on Saturday night released an unprecedented warning that ICE was about to begin arresting people. Schaaf said she issued the alert after receiving confidential tips from “credible sources,” and conferring with attorneys to make sure she wasn’t opening herself up to federal prosecution.

The mayor’s move endangered ICE officers and alerted their targets, Homan asserted, “making clear that this reckless decision was based on her political agenda.” He said 864 “criminal aliens and public safety threats remain at large in the community, and I have to believe that some of them were able to elude us thanks to the mayor’s irresponsible decision.”

Fox News, which was given a ride-along with ICE officers during the operation, reported that agency officials were asking the Department of Justice to investigate whether Schaaf broke any laws.

In a statement Tuesday night, Schaaf stood by her decision to go public.

“My statement on Saturday was meant to give all residents time to learn their rights and know their legal options. It was my intention that one mother, or one father, would use the information to help keep their family together,” the mayor said. “I do not regret sharing this information. 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.”

San Francisco Mayor Mark Farrell released a statement saying that the city won’t “cower” as the “administration pursues their political plan of haphazardly punishing sanctuary cities.”

“We stand with our hardworking, law-abiding immigrant neighbors and we are unified in our response to the divisive rhetoric of this president.”

The Chronicle reported in January that federal officials were planning the Northern California operation. The Trump administration has repeatedly expressed frustration at sanctuary laws in the state, which restrict cooperation between local authorities and ICE in an effort to convince undocumented immigrants they don’t need to live in the shadows.

Trump seized upon the killing of Steinle to argue that sanctuary policies are dangerous. The undocumented immigrant shooter, Jose Ines Garcia Zarate, had previously been released from San Francisco County Jail under the city’s sanctuary ordinance, even though immigration officers had asked that he be turned over for a sixth deportation.

This week’s sweep is the second to target California since a statewide sanctuary law signed by Gov. Jerry Brown, SB54, went into effect in January. The legislation, among other things, limits the circumstances in which jails across the state can turn over undocumented inmates to ICE and forbids police from arresting people on immigration warrants.

Earlier this month, ICE arrested more than 200 immigrants suspected of being undocumented in an operation in Los Angeles. Federal agents also told 122 businesses there that they would be checking whether their employees were authorized to work. ICE launched a similar action in Northern California in January, visiting 77 businesses.

“If you take all of the administration’s statements in context ... it suggests that this is highly politically motivated and meant to send a message to California,” said Pratheepan Gulasekaram, a professor and immigration expert at Santa Clara University School of Law. The message, he said, is that “not cooperating with federal immigration authorities will result in aggressive immigration enforcement.”

The ACLU of Northern California said Tuesday that reports from rapid-response networks over the previous three days suggested “that ICE enforcement is terrorizing communities of color. The targeting of cities and states that refuse to use their limited resources to fuel the Trump administration’s deportation machine is cruel and inhumane.”

ICE said the agency “focuses its enforcement resources on individuals who pose a threat to national security, public safety, and border security.” But officials also said ICE “no longer exempts classes or categories of removable aliens from potential enforcement.”

Among those arrested this week, ICE said in a statement, was a 38-year-old “documented Sureño gang member” with four previous deportations to Mexico and multiple criminal convictions, including for assault with a deadly weapon.

In Bay Point, officials said, officers arrested a man with eight past deportations and a conviction for assault with a deadly weapon, and in Stockton they arrested a man with a conviction for committing lewd acts on a child. ICE did not release a full list of those arrested.

The Northern California sweep began three days after Trump threatened to remove ICE officers from the state, saying, “In two months they’d be begging for us to come back.”