Washington — President Trump on Saturday delayed a wave of roundups of undocumented families which immigration authorities were expected to start carrying out Sunday. Mr. Trump nevertheless threatened to order mass deportations unless congressional Democrats agreed to revamp the nation's asylum laws within two weeks.

His stunning reversal came as immigrant advocates across major U.S. cities had been mounting an unprecedented campaign to prepare undocumented immigrants for a highly publicized operation in which Immigration and Customs Enforcement (ICE) was expected to target more than 2,000 families with pending deportations orders.

"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," Mr. Trump wrote on Twitter Saturday afternoon. "If not, Deportations start!"

Get Breaking News Delivered to Your Inbox

Democrats in Congress and in major U.S. urban centers — which were likely to be the main targets of the now-delayed operations — had urged the White House to abort any massive deportation blitz, which they believed would've separated families in which some members are undocumented but others, particularly children, are U.S. citizens.

Earlier Saturday, House Speaker Nancy Pelosi, a Democrat from California, made a last-ditch attempt to convince the president to halt the roundups — which she said would result in "collateral damage" to children, who could be U.S. citizens, of undocumented immigrants.

"Tomorrow is Sunday, and as many people of faith attend religious services, the President has ordered heartless raids. It is my hope that before Sunday, leaders of the faith-based community and other organizations that respect the dignity and worth of people will call upon the President to stop this brutal action which will tear families apart and inject terror into our communities," Pelosi wrote in a statement.

It is unclear if the president relented because of concerns raised by Democrats — as he claimed in his Twitter post — or because of the political damage the raids could've inflicted on his agenda. Republicans and Democrats in Congress are currently negotiating legislation to allocate funds to different agencies, including ICE, that are dealing with the large-scale migration of Central American families and unaccompanied children to the U.S.-Mexico border. Last month, border apprehensions hit a 13-year high.

Any massive deportation blitz would provoke significant public outcry and possibly derail negotiations in Congress, as Democrats — some of whom have called for ICE's abolishment — could refuse to sign-off on funding for any type of immigration enforcement as long as ICE targeted families with removal orders but no criminal history.

Although somewhat relieved, immigrant advocates said the president's unexpected announcement on Saturday just fueled more confusion and anxiety in immigrant communities.

Ana Maria Rea, a legislative affairs manager for RAICES, one of the pro-immigrant groups spearheading efforts to inform immigrants of their rights ahead of the expected raids, accused Mr. Trump of using threats to deport families to advance his hardline immigration agenda in Congress.

"It's really sad and it's really sickening that the president uses suffering, torture and fear tactics as a bargaining chip," she said. "These are real people with real lives that haven't been able to sleep for the past three days ever since he announced what he was going to do."

On Saturday evening, ICE spokesperson Carol Danko released a new statement praising the president for his decision and denouncing leaks to the press regarding the planned roundups.

"Any leak telegraphing sensitive law enforcement operations is egregious and puts our officers' safety in danger," Danko wrote in a statement.

"U.S. Immigration and Customs Enforcement (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," she added.

Last week, Mr. Trump pledged to start deporting "millions" of undocumented immigrants in the coming week — a claim that had been partially confirmed by ICE officials, who were unusually forthcoming about some of the details about the large-scale operation.

As part of an effort by the administration to send a "powerful message" of deterrence to families in Central America — which have journeyed north towards the U.S. in record numbers the past few months — ICE had been expected to carry out a series of operations in major U.S. cities to apprehend and deport families who received an order of removal from a judge.

This week, the acting ICE director Mark Morgan told reporters his agency wanted to uphold the values of "humanity, compassion and dignity" but that it was also critical to prevent what he portrayed as the erosion of the rule of law.

"I don't want to send ICE agents to their workplace, I don't want to send ICE agents to their homes. I don't want to send ICE agents to try to track them down and apprehend them in their communities, in their towns," he added. "That's not what I prefer to do. But we have applied due process. And we've tried to work with them. We've tried and attempted to say, 'Hey, come turn yourself in.' But they have refused to do so. So we have no choice but to carry out our statutory mandated job."

Although the president claimed last week that "millions" would be deported under a new wave of raids, such an operation would be logistically impossible given the resources and manpower ICE has at its disposal. There are currently approximately 10.5 million undocumented immigrants living in the U.S.

Last year, ICE removed more than 250,000 people. The highest number of yearly deportations came during the Obama administration in 2012, when the agency removed approximately 410,000 immigrants.