(Adds New York City mayor's comment)

NEW YORK, April 12 (Reuters) - Democratic U.S. mayors said on Friday their cities would welcome illegal immigrants, dismissing President Donald Trump's threats to transport people detained at the border to "sanctuary cities" as illustrating the White House's callous approach to the issue.

Trump confirmed on Twitter that he wanted to transport people detained in his immigration crackdown at the U.S.-Mexico border to sanctuary cities, an informal designation for localities that refrain from assisting federal immigration authorities in detaining people living in the country illegally.

Mayors from across the country were quick to respond to Trump's latest portrayal of immigrants and sanctuary cities as threats.

In New York City, where nearly 40 percent of the population are immigrants, Mayor Bill de Blasio said Trump's immigration policy was rooted in cruelty.

"He uses people like pawns," de Blasio said in a statement. "New York City will always be the ultimate city of immigrants – the President's empty threats won't change that."

In Philadelphia, known as the city of brotherly love, Mayor Jim Kenney said in a statement that his city "would be prepared to welcome these immigrants just as we have embraced our immigrant communities for decades." He said the White House was demonstrating "the utter contempt that the Trump Administration has for basic human dignity."

The Republican president has made cracking down on illegal and legal immigration a centerpiece of his administration, and has regularly threatened to try to cut federal funding to programs in generally Democratic-leaning sanctuary cities, counties and states.

"Due to the fact that Democrats are unwilling to change our very dangerous immigration laws, we are indeed, as reported, giving strong considerations to placing Illegal Immigrants in Sanctuary Cities only," Trump wrote on Twitter, confirming a Washington Post report.

The mayor of Los Angeles, Eric Garcetti, responded by saying on Twitter: "These are people, not pawns, Mr. President."

At least one governor, New Mexico's Michelle Lujan Grisham, weighed in, calling the plan "absurd, sad and all too characteristic of the president — not to mention indicative of a complete and cruel indifference to the plight of migrant families."

The mayors of Oakland, California, and Takoma Park, Maryland, voiced similar reactions.

Trump's latest move on immigration comes days after U.S. officials said they arrested or denied entry to over 103,000 people along the border with Mexico in March, more than twice as many as the same period last year.

"I am shocked but not surprised that once again this president is playing a cynical game with people's lives in order to score political points," Jesse Arreguin, the mayor of Berkeley, California, said in a statement. "Rather than supporting a real pathway to citizenship for the millions of immigrants in this country, he is fanning the flames of division."

(Reporting by Jonathan Allen; editing by Jonathan Oatis and Leslie Adler)

Our Standards: The Thomson Reuters Trust Principles.