Escalating California’s resistance to federal immigration enforcement, Oakland’s mayor has warned residents that she believes an operation was imminent.

“I am sharing this information publicly not to panic our residents but to protect them,” Oakland Mayor Libby Schaaf said in a press release, citing her “moral obligation” and directing people to immigration law resources.

“I know that Oakland is a city of law-abiding immigrants and families who deserve to live free from the constant threat of arrest and deportation,” she added, saying immigration authorities have “used activity rumors in the past as a tactic to create fear”.

A spokesman for Immigration and Customs Enforcement (ICE) said in a statement that deportation officered “conduct targeted enforcement operations on a daily basis in Northern California and across the nation”.

The extraordinary heads-up from the head of one of California’s largest cities highlighted the determination by much of the state’s leadership to stymie the Trump administration’s immigration crackdown. California has the largest population of immigrants in the country illegally.

Cities and the state legislature have sought to shield some of them from deportation by blocking cooperation with federal authorities. Cities have also backed a variety of immigration assistance initiatives, with Oakland funding a rapid-response network that operates a hotline allowing people to report ICE activity and seek help fighting deportation.

Protestors rally at JFK Airport against Muslim immigration ban Show all 20 1 /20 Protestors rally at JFK Airport against Muslim immigration ban Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-1 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-2 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-3 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-4 SAN FRANCISCO, CA - JANUARY 28: Demonstrators hold signs during a rally against a ban on Muslim immigration at San Francisco International Airport on January 28, 2017 in San Francisco, California. President Donald Trump signed an executive order Friday that suspends entry of all refugees for 120 days, indefinitely suspends the entries of all Syrian refugees, as well as barring entries from seven predominantly Muslim countries from entering for 90 days. Stephen Lam/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-5 A crowd of protesters gathers outside of the Brooklyn Federal Courthouse as a judge hears a challenge against President Donald Trump's executive ban on immigration from several Muslim countries, on January 28, 2017 in Brooklyn. The judge issued an emergency stay on part of Trump's executive order, ruling that sending refugees stopped at U.S. airports back to their countries would be harmful. Yana Paskova/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-6 Protestors rally during a demonstration against the new immigration ban issued by President Donald Trump at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-7 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the new immigration ban issued by President Donald Trump at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-8 Protestors rally during a demonstration against the new immigration ban issued by President Donald Trump at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-9 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. (Photo by Stephanie Keith/Getty Images) Getty Images Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-10 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. (Photo by Stephanie Keith/Getty Images) Getty Images Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-11 NEW YORK, NY - JANUARY 28: Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-12 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-13 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-14 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-15 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-16 Protestors rally during a demonstration against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump signed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-17 NEW YORK, NY - JANUARY 28: Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-18 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-19 Protestors rally during a protest against the Muslim immigration ban at John F. Kennedy International Airport on January 28, 2017 in New York City. President Trump singed the controversial executive order that halted refugees and residents from predominantly Muslim countries from entering the United States. Stephanie Keith/Getty Protestors rally at JFK Airport against Muslim immigration ban jfk-protest-muslim-ban-20 Passengers wait in line to check in at the American Airlines terminal at JFK International Airport August 10, 2006 in the Queens borough of New York City. British authorities arrested 21 people and halted a anallegedly terrorist plot to use liquid explosives concealed in carry-on luggage to blow up airliners traveling between Britain and the U.S. Homeland Security chief Michael Chertoff said that the plot appeared to be directed at U.S. carriers flying out of Heathrow. such as United Airlines, American Airlines, Continental Airlines. Stephen Chernin/Getty

Those efforts have made the state a recurring target for Donald Trump, who threatened last week to halt ICE activity there, saying crime would soar as a result. Senior ICE officials have also warned that California’s restrictions will make it harder to target specific immigrants for arrests and lead to more people being swept up.

Donald Trump reads poem The Snake at CPAC 2018

“While the vast majority of cities in America do cooperate with ICE, others force ICE to assign additional resources to conduct at-large arrests in the community, putting officers, the general public and the aliens at greater risk and increasing the incidence of collateral arrests,” ICE spokesman James Schwab said in response to Ms Schaaf’s warning. “Sanctuary cities and states are not immune from federal law”.

Immigrant advocates accuse the Trump administration of an indiscriminate crackdown that deports both serious criminals and unauthorised immigrants with no criminal records, pointing to a spike in ICE arrests of immigrants not convicted of any crimes.