The effort comes weeks after President Donald Trump had tweeted ICE's plans to conduct the raids, then delayed the operation after additional details became public. The President, adamant on doubling down on illegal immigration, has repeatedly tweeted about an impending operation, a striking move given that operations are not announced ahead of time.
It comes in the middle of another tumultuous week at the White House, with controversy surrounding Labor Secretary Alex Acosta and concerns about upcoming testimony of former special counsel Robert Mueller. Trump is also trying to press ahead with adding a question about citizenship to the 2020 census after the Supreme Court dealt a major setback last month.
Matthew Bourke, an ICE spokesman, said ICE will not comment on operational details and "ICE prioritizes the arrest and removal of unlawfully present aliens who pose a threat to national security, public safety and border security."
"They're absolutely going to happen. There's approximately a million people in this country with removal orders. And of course that isn't what ICE will go after in this, but that's the pool of people who have been all the way through the due process chain," he told reporters at the White House.
The raids were expected in Atlanta, Baltimore, Chicago, Denver, Houston, Los Angeles, Miami, New Orleans, New York and San Francisco.
After the original raids were delayed, Acting ICE Director Mark Morgan said operational details that had been reported were to blame. Morgan had previously confirmed to reporters that plans were underway, though he refrained from providing a time frame or details on the scope of the operation.
Former acting ICE director John Sandweg, who served under the Obama administration, also expressed concern Thursday about operational details being released ahead of time.
"You never want the target to know you're coming. You want that element of surprise because it keeps you safe," he said, referring to the officers.
"From an effective perspective, that's why you don't announce these things," he added. "Somebody has determined the political value of talking about this publicly exceeds the operational value of surprise."
House Speaker Nancy Pelosi reiterated her call Thursday for evangelicals to step in and urge the President not to carry out ICE raids on Sunday.
Last month, Pelosi spoke with Trump by phone to urge him not to go through with the planned actions. She also credited faith-based organizations with reaching out to Trump and influencing him.
"This brutal action will terrorize children and tear families apart," she said.
Pelosi said the President also sent Republican Sen. Lindsey Graham to her office to talk about longer term solutions for the border.
"In terms of comprehensive immigration I think there's real need for it," she said. "My understanding is that people don't even like that term anymore so we're talking about dream promise and beyond, where we go with it, and I think that is something that we have to do. It's not something that we can do in two weeks.
This story is breaking and will be updated.
CNN's Betsy Klein, Pamela Brown, Joe Johns, Ashley Killough, Clare Foran and Naome Seifu contributed to this report.