This post has been updated.

President Obama said in a video that he will lay out his proposal to overhaul the nation's immigration system Thursday and will travel to Las Vegas on the heels of that announcement to rally support for his initiative on Friday.

"Tomorrow night I'm going to be announcing here from the White House some steps I can take to start fixing our broken immigration system," Obama said in a video posted on Facebook Wednesday afternoon.

"Everybody agrees that our immigration system is broken. Unfortunately Washington has allowed the problem to fester for too long," Obama said. "So what' I'm going to be laying out is the things I can do with my lawful authority as president to make the system work better even as I continue to work with Congress and encourage them to get a bipartisan, comprehensive bill that can solve the entire problem.

According to a senior Democrat familiar with the plans, Obama will announce on Thursday that he is providing temporary protections to up to 5 million undocumented immigrants. His orders will make up to 4 million undocumented immigrants eligible for temporary protective status and provide relief to another 1 million through other means.

In a blow to activists advocating on behalf of young immigrant families, there will be no guaranteed protections for the parents of so-called “Dreamers,” -- children protected by Obama’s 2012 Deferred Action for Childhood Arrivals program – nor for immigrant agricultural workers, said the Democrat, who was not authorized to speak publicly on the matter.

Congress will receive official details on the move Thursday, according to a senior Democratic Party official.

Obama said he will travel to Del Sol High School in Las Vegas Friday, where he will discuss and rally support for his plan.

Advocates began readying events to promote the administration’s immigration policy.

“We hear there will be a prime time Thursday evening announcement (to preview) and full unveiling in Vegas on Friday,” immigration advocate Dawn Le told other activists in an e-mail, which was later inadvertently sent to a group of reporters Wednesday morning. “Can folks begin to work and plan watch parties for Thursday and/or Friday? Unclear whether Thursday night content will be what is "celebratory," but Friday will be where we need a lot of energy guaranteed.”

Obama launched his push for immigration reform in January 2013 in Las Vegas, outlining a plan that would allow many of the nation’s 11 million undocumented immigrants to earn citizenship.

The president's decision to speak at the city's Del Sol High School highlights the administration's intensified push to convince Latinos that the Democratic Party is committed to addressing the dilemma of millions of undocumented immigrants. Obama is preparing to use his executive authority to expand temporary protections to millions of these individuals, as well as to broaden visa programs for highly skilled technology workers and perhaps also stiffen security along the U.S.-Mexico border.

During an appearance at the National Press Club Wednesday, Department of Homeland Security Secretary Jeh Johnson said Obama will announce "in the coming days ... [a] set of comprehensive reforms, within our existing legal authorities, to fix our broken immigration system."

He did not specify the actions Obama will take but did say they will include steps to further secure the southwestern border of the United States. Administration lawyers have concluded that executive action on the issue is legal and within the president's authority, he said, despite intense opposition from Republicans.

"Legislative action is always preferable," Johnson said. "But we have waited for Congress to act, and the Congress has not acted. The president has waited."

Johnson said the administration has concluded it has "wide latitude" to take action. "It can't be that we're not allowed to lift a finger to fix our broken immigration system," he said. "And we will."

Congressional Republicans have warned Obama that he risks undermining the prospects for cooperation on legislation in the final two years of his presidency if he takes action on immigration.

The decision to speak in Las Vegas could also bolster the political standing of Senate Majority Leader Harry M. Reid (D-Nev.), who said in an interview with Univision on Tuesday that when it came to expanding protections for undocumented immigrants, "I think it should be done now."

Ali Noorani, executive director of the National Immigration Forum, wrote in an e-mail that even as Obama acted on his own to break the stalemate on the issue, Republicans would still have a chance to legislate.

“While executive action is not ideal, it accomplishes four things: Stabilizes our workforce, prioritizes law enforcement, protects families and puts congressional Republicans in the driver’s seat going into 2015," Noorani wrote. "They have an incredible opportunity to get credit for fixing America’s immigration system.”

With Obama likely on the verge of making an announcement, Sen. Mitch McConnell (R-Ky.), the soon-to-be majority leader, expressed confidence Wednesday that congressional Republicans will extend funding for the federal government, which is set to expire next month, even if the president moves to overhaul the immigration system and some conservatives call for a spending showdown.

But in a sign that GOP strategy is still being formulated, McConnell did not specify the framework and length of possible funding legislation. Republican leaders in the House and Senate are still mulling a variety of options, all while hoping to avoid a politically damaging shutdown.

“We have two goals here at the end of the session: fund the government and avoid retroactive tax increases. I’m confident that we’ll do both,” McConnell said in a brief exchange at the U.S. Capitol.

Other congressional Republicans warned again that Obama risks his relationship with a GOP-controlled Capitol Hill if he acts.

“If ‘Emperor Obama’ ignores the American people and announces an amnesty plan that he himself has said over and over again exceeds his Constitutional authority, he will cement his legacy of lawlessness and ruin the chances for Congressional action on this issue -- and many others,” Michael Steel, a spokesman for House Speaker John A. Boehner (R-Ohio), said in an e-mail.

In an effort to cast doubts on the legality of Obama’s decision, GOP aides have been circulating a list of 22 times the president has said publicly that he doesn’t believe he has the authority to act through executive action to change immigration laws.

Correction: This report incorrectly attributed strategy comments to AFL-CIO spokesman Jeff Hauser rather than immigration advocate Dawn Le.

Tom Hamburger, Jerry Markon, Robert Costa and Paul Kane contributed to this report.