Former US president Barack Obama has censured his successor over ending an amnesty for 800,000 people brought to America illegally as children.

In a rare and lengthy statement following the end of his tenure, the first African American president described Trump’s move as “wrong,” “self-defeating” and “cruel.”

“To target these young people is wrong — because they have done nothing wrong. It is self-defeating — because they want to start new businesses, staff our labs, serve in our military, and otherwise contribute to the country we love. And it is cruel… It’s a political decision, and a moral question,” Obama wrote on Tuesday. “Whatever concerns or complaints Americans may have about immigration in general, we shouldn’t threaten the future of this group of young people who are here through no fault of their own, who pose no threat, who are not taking away anything from the rest of us.”

His vice president, Joe Biden, has also reacted to the move by taking to Twitter.

“Brought by parents, these children had no choice in coming here. Now they’ll be sent to countries they’ve never known. Cruel. Not America,” he tweeted.

Obama had previously said that he would rarely speak out after the end of his term, yet warning that revoking the program, called Deferred Action for Childhood Arrivals (DACA), would be among actions that would make him react.

“The notion that we would just arbitrarily or because of politics punish those kids, when they didn’t do anything wrong themselves, I think would be something that would merit me speaking out,” he said ahead of leaving office in January.

The program, Obama’s chief legacy item in immigration, was aimed at shielding the children of undocumented immigrants from deportation, but Trump decided to end it, arguing that it was legally flawed, and that native-born Americans must be prioritized.

“Let’s be clear: the action taken today isn’t required legally,” said the former president. “It’s up to members of Congress to protect these young people and our future.”

Trump ended the program, introduced during Obama’s first term in 2012, but called on Republican-controlled Congress to pass legislation aimed at letting the so-called “Dreamers” stay in the US.

Attorney General Jeff Sessions announced the president’s decision earlier in the day, calling the program an “open-ended circumvention of immigration laws.”

“The program known as DACA that was effectuated under the Obama administration is being rescinded,” Sessions told reporters. “The policy was implemented unilaterally, to great controversy and legal concern.”

He added that “the executive branch through DACA deliberately sought to achieve what the legislative branch specifically refused to authorize on multiple occasions.”

The decision has caused outraged among activists, leading to protests in some cities, including Washington, DC, and New York.

Trump himself released a statement, saying that he does not support “punishing children, most of whom are now adults, for the actions of their parents. But we must also recognize that we are nation of opportunity because we are a nation of laws.”

“I have advised the Department of Homeland Security that DACA recipients are not enforcement priorities unless they are criminals, are involved in criminal activity, or are members of a gang,” he added.

The Republican president has vowed to crack down on immigration but has failed to get his complete agenda through so far.