Washington (CNN) President Donald Trump announced Saturday that he's delaying for two weeks US Immigration and Customs Enforcement raids that were planned to take place Sunday in 10 major US cities, saying deportations will proceed unless Congress finds a solution on the US-Mexico border.

The President's pullback was an about-face in a matter of hours on enforcing his signature immigration policy, following deep criticism from the cities' mayors, top Democrats and immigration activists who called the coordinated arrests and deportations on targeted migrant families "heartless."

"At the request of Democrats, I have delayed the Illegal Immigration Removal Process (Deportation) for two weeks to see if the Democrats and Republicans can get together and work out a solution to the Asylum and Loophole problems at the Southern Border,'" Trump said on Twitter Saturday. "If not, Deportations start!"

At the request of Democrats, I have delayed the Illegal Immigration Removal Process (Deportation) for two weeks to see if the Democrats and Republicans can get together and work out a solution to the Asylum and Loophole problems at the Southern Border. If not, Deportations start!

Acting ICE Director Mark Morgan blamed leaked details for the raids' delay, but did not specify what information was disclosed or by who.

"The media got ahold of some operational specifics ... and they report it," Morgan told Fox News host Jeanine Pirro Saturday.

"It's just egregious, and it puts the lives of the officers and agents at risk," he added. "The men and women I've served with are true American heroes. And so what the President did -- he recognized that, and so he postponed ... to protect them."

House Speaker Nancy Pelosi called Trump Friday night and asked him to call off the ICE deportation raids, a source familiar with the call tells CNN. The two spoke for about 12 minutes.

White House deputy press secretary Judd Deere confirmed to CNN that a phone call took place.

On Saturday, Pelosi pushed for Trump to halt the raids in a statement, calling the anticipated operation "heartless" and a "brutal action which will tear families apart and inject terror into our communities."

"These families are hard-working members of our communities and our country. The President's action makes no distinction between a status violation and committing a serious crime," Pelosi said.

After Trump's announcement was made, Pelosi tweeted, "Mr. President, delay is welcome. Time is needed for comprehensive immigration reform. Families belong together."

Earlier in the day, Trump defended the raids, arguing that the targeted families have been dodging the law.

"The people that Ice will apprehend have already been ordered to be deported," Trump tweeted. "This means that they have run from the law and run from the courts. These are people that are supposed to go back to their home country. They broke the law by coming into the country, & now by staying."

The people that Ice will apprehend have already been ordered to be deported. This means that they have run from the law and run from the courts. These are people that are supposed to go back to their home country. They broke the law by coming into the country, & now by staying. — Donald J. Trump (@realDonaldTrump) June 22, 2019

A senior Democratic aide says Trump is "trying to create leverage in a situation where he has none," adding "it won't work."

"Democrats aren't going to compromise their values. He's walked away from several deals on immigration. We have no illusions here," the aide said.

'They will be removed from the country'

Trump told reporters as he departed the White House for Camp David Saturday that the raids would begin "during the course of this next week, maybe even a little bit earlier than that."

"These are people that came into the country illegally. They've been served. They've gone through a process. A process of the courts, and they have to be removed from the country," Trump said. "They will be removed from the country."

He characterized the deportation raids as "very good law enforcement people going by the law," and claimed that his administration is "very focused on getting MS-13 out of this country."

"Some cities are going to fight it, but if you notice, they're generally high crime cities. If you look at Chicago, they're fighting it. If you look at other cities, they're fighting it. Many of those cities are high crime cities and they're sanctuary cities," Trump said. "People are tired of sanctuary cities and what it does and the crime it brings."

Raids had been planned in Atlanta, Baltimore, Chicago, Denver, Houston, Los Angeles, Miami, New Orleans, New York and San Francisco.

Trump made a vague announcement on Monday that an ICE operation was imminent. He claimed that his administration would be deporting "millions" of undocumented immigrants next week -- disclosing such an operation before it was carried out and surprising some officials within his own administration.

Tension within the Trump administration

Acting Department of Homeland Security Secretary Kevin McAleenan was hesitant about elements of the operation, two sources familiar with his thinking told CNN.

CNN reported last month that the administration had been considering deporting migrant families. A source told CNN at the time that McAleenan was resistant to the plan, concerned in part that it could hurt negotiations with congressional Democrats for ICE funding, which has been strapped for resources, as well as the political optics.

According to a source familiar with the situation, McAleenan on Friday pulled out of a planned Sunday show appearance on the day the ICE operation was slated to begin, adding to speculation that there's a split with the White House.

A separate source told CNN that McAleenan was at the White House Friday and "not in a good way."

An ardent supporter of Trump's immigration policies, Tom Homan, the former ICE director and now a FOX News contributor, seemed to suggest Saturday that McAleenan leaked information about the ICE operation to media. CNN has reached out to McAleenan for comment.

"You got the Acting Secretary of Homeland Security resisting what ICE is trying to do. In the Washington Post, in numerous media outlets, he does not support this operation," Homan said on Fox News, adding, "This leak, which I know where it came from, we all know where it came from. That story only benefits one person, put these officers at greater risk of harm."

Homan, who Trump named "border czar" but has not yet accepted the job, has previously backed McAleenan.

An ICE spokesperson responded Saturday, saying, ""Any leaks telegraphing sensitive law enforcement operations is egregious and puts our officers' safety in danger. ICE officers are true American Heroes and the President's postponement protects officers and provides an opportunity for Congress to swiftly work together in a bipartisan fashion to end the incentives for child smuggling and ensure all illegal aliens can be promptly returned upon apprehension at the Southern Border."

Mayors fight back

On Friday, the cities' mayors spoke out against the raids and expressed support for the migrant families.

"It is unconscionable that the Federal administration is targeting innocent immigrant families with secret raids that are designed to inflict as much fear and pain as possible," said San Francisco Mayor London Breed, who leads a sanctuary city.

Some of the mayors, including Chicago's Lori Lightfoot and Los Angeles Mayor Eric Garcetti, said their city would not assist in the immigration raids.

"No Angeleno should ever have to fear being snatched from their home or separated from their loved ones — and we are doing everything we can to provide immigrant families with the information and support they need," Garcetti said in a statement.

Acting ICE chief Mark Morgan told reporters Wednesday that the goal was "not to separate families," but to deter migrants from illegally crossing the southern border.

Migrant families, who had received final orders of removal by judges in absentia, were sent letters in February from ICE, asking them to self-report to local ICE offices by March to comply with the orders, Morgan said.

He said ICE and the Justice Department had worked closely together on the family expedited docket and that the "results were very disappointing," claiming that some families failed to show up for their immigration hearings.

Before Trump's Saturday announcement, field agents at local offices were receiving briefings and trainings, according to a senior immigration official. There were also preparations in place for mixed-immigration status families: for example, if a parent is undocumented, but has a US citizen child.

"Due to law-enforcement sensitivities and the safety and security of U.S. Immigration and Customs Enforcement personnel, the agency will not offer specific details related to ongoing enforcement operations before the conclusion of those actions," ICE said in a statement Friday.

In the later years of Barack Obama's presidency, the Department of Homeland Security deployed an operation targeting family units due to the uptick in families and unaccompanied minors attempting to cross the border, after initially focusing on felons. It was revived in Trump's first year in office.

This story has been updated.