The Trump administration issued a double threat Monday to sanctuary cities and states, warning it would withhold criminal-justice grants to those that don’t cooperate with immigration authorities and “claw back” monies already allocated.

Attorney General Jeff Sessions said the crackdown — which would be a direct hit on both New York City and New York state — was necessary to protect US citizens from those undocumented immigrants who are dangerous criminals.

“Countless Americans would be alive today and countless loved ones would not be grieving today if these policies of sanctuary cities were ended,” Sessions said at the White House.

He cited as one example the 2015 murder of Kate Steinle in San Francisco by a repeat felon who entered the United States illegally.

New York City and state have both declared they won’t cooperate with routine deportation requests and stand to lose tens of millions of dollars.

“President Trump’s latest threat changes nothing,” said Mayor de Blasio in a statement.

“Any attempt to cut NYPD funding for the nation’s top terror target will be aggressively fought in court.”

Nationwide, $4.1 billion in grants will be awarded this year between the Office of Justice Programs and Community Oriented Policing Services, Sessions said.

The Justice Department didn’t say how far back it would seek to “claw back” funds.

But both the city and state have been major beneficiaries of Justice Department grants, with the state Office of Victim Services alone receiving $134 million in 2016.

The Sessions announcement largely mirrors an Obama administration policy announced in February 2016 to withhold funds from cities that wouldn’t cooperate with federal immigration authorities.

The policy was scheduled to take effect in the current fiscal year. A Justice Department official said no jurisdiction lost money for disobeying the policy under Obama. Programs affected include the State Alien Assistance, which shipped $11.6 million to the city and $10.4 million to the state in 2015.

Any attempt to claw back or withhold federal funds would almost certainly meet aggressive legal challenges.

“You are coming close to essentially putting a gun to the head of jurisdictions,” said Tom Jawetz, vice president of immigration at the Center for American Progress.

Holding sanctuary cities accountable was a major campaign promise for Trump.

Municipal leaders from around the country gathered in Manhattan on Monday and vowed to defy Trump’s crackdown on sanctuary cities.

“We are going to become this administration’s worst nightmare,” City Council Speaker Melissa Mark-Viverito said.