Spurning furious Republicans, U.S. President Barack Obama unveiled expansive executive actions on immigration Thursday night to spare from deportation nearly five million people in the U.S. illegally and to refocus enforcement efforts on "felons, not families."

The moves, affecting mostly parents and young people, marked the most sweeping changes to the nation's fractured immigration laws in nearly three decades and set off a fierce fight with Republicans over the limits of presidential powers.

In a televised address to the nation, Obama defended the legality of his actions and challenged Republican lawmakers to focus their energy not on blocking his actions but on approving long-stalled legislation to take its place.

U.S. Speaker of the House John Boehner pledged Friday morning to fight Obama's plan, telling reporters the president had "turned a deaf ear" to the electorate and "deliberately sabotaged" efforts at bipartisan immigration reform.

Boehner said the reforms would encourage more people to come to the U.S. illegally. Separately, House Republicans sued the Obama administration on Friday over its implementation of the president's health-care law, claiming he had overstepped his authority.

The administration is also setting new immigration enforcement priorities that could make it easier for many more people in the U.S. illegally to stay in the country.

U.S. Speaker of the House John Boehner pledged Friday morning to fight Obama's plan, telling reporters the president had and 'deliberately sabotaged' efforts at bipartisan immigration reform. (Larry Downing/Reuters) "There are actions I have the legal authority to take as president — the same kinds of actions taken by Democratic and Republican presidents before me — that will help make our immigration system more fair and more just," Obama said.

Obama said deportations of criminals are up 80 per cent and that the government will keep focusing enforcement resources on actual threats to the U.S.

"Felons, not families. Criminals, not children. Gang members, not a mom who’s working hard to provide for her kids. We’ll prioritize, just like law enforcement does every day.

The president said that tracking down, rounding up and deporting millions of people isn’t realistic. Obama offered temporary residence for those who have been in the U.S. for more than five years, or have children who are American citizens or legal residents.

"If you register, pass a criminal background check, and you're willing to pay your fair share of taxes — you’ll be able to apply to stay in this country temporarily, without fear of deportation. You can come out of the shadows and get right with the law."

Obama insisted that his actions did not amount to amnesty.

Fate of millions still unresolved

"Amnesty is the immigration system we have today — millions of people who live here without paying their taxes or playing by the rules, while politicians use the issue to scare people and whip up votes at election time," he said

However, the plan would leave the fate of millions more unresolved. With more than 11 million immigrants living in the country illegally, Obama's actions would not offer specific protections to more than half.

President Barack Obama unveiled expansive executive actions on immigration Thursday night to spare nearly five million people in the U.S. illegally from deportation. (Jim Bourg/Associated Press)

But the vehement reactions of Republicans, who will have control of Congress come January, made clear that Obama was courting a serious partisan confrontation.

Boehner, who has refused to have his Republican members vote on broad immigration legislation passed by the Senate last year, said Obama's decision to go it alone "cemented his legacy of lawlessness and squandered what little credibility he had left."

Actions could be reversed

None of those affected by Obama's actions would have a direct path to citizenship, and his actions could be reversed by a new president after he leaves office. Moreover, officials said the eligible immigrants would not be entitled to federal benefits — including health-care tax credits — under Obama's plan.

Obama's plan would leave the fate of millions more unresolved. With more than 11 million immigrants living in the country illegally, Obama's actions would not offer specific protections to more than half. (Jacquelyn Martin/Associated Press)

Some immigrant advocates worried that even though Obama's actions would make millions eligible for work permits, not all would participate out of fear that Republicans or a new president would reverse the executive orders.

"If the reaction to this is that the Republicans are going to do everything they can to tear this apart, to make it unworkable, the big interesting question will be, will our folks sign up knowing that there is this cloud hanging over it," said Janet Murguia, president and CEO of the National Council of La Raza.