US Attorney General Jeff Sessions on Monday urged the country's so-called "sanctuary cities" to once again begin cooperating with federal authorities to detain and deport undocumented migrants and immigrants who have committed crimes.

"I strongly urge our nation's states and cities and counties to consider carefully the harm they are doing to their citizens by refusing to enforce our immigration laws and to rethink these policies. Such policies make their cities and states less safe, public safety as well as national security are at stake, and put them at risk of losing federal dollars," said Sessions, who made an unannounced appearance at the daily White House press briefing.

 "The American people want and deserve a lawful system of immigration that keeps us safe, and one that serves the national interests. This expectation is reasonable, just and our government has the duty to meet it and we will meet it," he added.

Sessions announced that the states, counties and cities seeking subsidies from Department of Justice will have to show that they are complying with federal law and pursuing immigrants who have committed crimes or who entered the country illegally.

The Justice Department subsidies include funds for training local police and for acquiring new equipment, including body cameras to be worn by law enforcement officers.

President Donald Trump in January signed an executive order to revive cooperation programs among the local police and immigration authorities and to halt the granting of certain federal funds to sanctuary cities, which includes about 200 metropolitan areas, counties and other US jurisdictions that protect immigrants from deportation.

Top officials in the sanctuary cities, including New York Mayor Bill de Blasio, have rejected Trump's proposals and have said that their cities will continue to be sanctuaries.

The sanctuary cities are refusing to inform the government of the immigration status of detained or arrested people to prevent their deportation.