Attorney General Jeff Sessions is reinforcing threats to go after sanctuary cities, warning the administration may withhold federal crime-fighting funds for four places struggling with gun violence.

It is the latest threat made by Sessions in his public campaign to force cooperation between local authorities and federal immigration officials.

The Justice Department sent letters to police departments in Baltimore, Md., Albuquerque, N.M., Stockton and San Bernardino, Calif. telling them if they wanted federal help to root out drug trafficking and gang crime, they’d have to work with federal immigration authorities.

Among other things, the Justice Department said they must give the authorities access to jails and provide advance notice before releasing someone in custody who is wanted on immigration violations.

The four cities targeted had all expressed interest in the DOJ’s new Public Safety Partnership, which enlists federal agents, analysts and technology to help communities find solutions to crime.

“Based on our review, we have concluded that your jurisdiction has levels of violence that exceed the national average, that your jurisdiction is ready to receive the intensive assistance the Department is prepared to provide, and that your jurisdiction is taking steps to reduce its violent crime,” the Aug. 3 letter said.

The letter sent by the DOJ to the four prospective cities’ police departments also asks them for proof of their compliance to step up efforts to help detain and deport people in the United States illegally. The deadline is Aug. 18.

Separately last week, Sessions told jurisdictions they need to meet the same conditions or lose out on millions of dollars from a separate program that aims to send grant money to support law enforcement.

The attorney general rolled out the rules as part of his promised crackdown on sanctuary cities.

His threat didn’t sit well with some – prompting a defiant pushback on the request.

Under old rules, cities seeking grant money needed only to show that they weren't prohibiting local law enforcement from communicating with immigration authorities.

Police use the money for everything from bulletproof vests to body cameras.

Sessions unveiled the policy amid speculation about whether he would retain his job following President Trump's blistering public criticism for his recusal from the Russia probe. The terse warning from the president seems, for now, to have subsided.

The Associated Press contributed to this report.