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.

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