President Donald Trump speaks during a meeting of the National Space Council in the East Room of the White House, June 18, 2018, in Washington, as Vice President Mike Pence looks on.
President Donald Trump speaks during a meeting of the National Space Council in the East Room of the White House, June 18, 2018, in Washington, as Vice President Mike Pence looks on.

WHITE HOUSE - "The United States will not be a migrant camp and it will not be a refugee holding facility," President Donald Trump vowed Monday amid growing outrage over his administration forcibly separating children from parents at the U.S. border with Mexico.

Trump, speaking in the White House East Room during a National Space Council meeting, warned that "what's happening in Europe … we can't allow that to happen to the United States — not on my watch."

WATCH: Trump on Immigration

Earlier in the day, on the Twitter social media platform, the president inaccurately linked migration in Germany to a rising crime rate. In actuality, the latest German government statistics show reported crimes at the lowest level in 30 years.

Tough border enforcement in the U.S. has led to the family breakups, with nearly 2,000 children being sent to mass detention centers or foster care from mid-April to the end of May, according to government officials.

The regular White House briefing was delayed several times Monday amid the furor as officials huddled with Trump in the West Wing.

'Zero-tolerance' policy

Press Secretary Sarah Sanders finally introduced Department of Homeland Security Secretary Kirstjen Nielsen after 5 p.m., and she defended the administration's "zero-tolerance" policy that is breaking up families at the southwestern U.S. border.

Department of Homeland Security Secretary Kirstjen
Department of Homeland Security Secretary Kirstjen Nielsen speaks during the daily briefing at the White House in Washington, June 18, 2018.

Nielsen forcefully pushed back at the negative media coverage, asserting that what U.S. authorities are doing is properly enforcing the law.

"What has changed is that we no longer exempt entire classes of people who break the law," she said.

Asked about critics accusing the administration of using children as "pawns" to demand legislative actions from Congress, the DHS secretary replied, "I say that is a very cowardly response," adding it is clearly within Congress' power "to make the laws and change the laws. They should do so."

Trump's Republican party controls both chambers in Congress, and the family border policies were set by his administration.

In a tweet displaying photographs of a detention facility, showing children sleeping on mats with foil blankets, Democrat Senator Tim Kaine wrote: "The real Trump Hotel." 

Kaine, a member of a subcommittee on children and families, was his party's vice-presidential nominee on the ticket with Hillary Clinton, which lost to Trump and Mike Pence in 2016.

Kamala Harris, one of the two Democratic Party senators from California, the country's most populous state, called Monday for Nielsen's resignation.

Harris, mentioned as a likely presidential candidate in 2020, said that under Nielsen's watch "our government has committed human rights abuses by breaking up families along the southern border. And she has failed to be accountable and transparent with the American people."

House Minority Leader Nancy Pelosi also added her voice to those calling for Nielsen to quit her post.

Both Nielsen and Attorney General Jeff Sessions, in speeches to a law enforcement group in New Orleans earlier Monday, defended the administration's stance.

U.S. Attorney General Jeff Sessions speaks at the
U.S. Attorney General Jeff Sessions speaks at the National Sheriffs' Association convention in New Orleans, June 18, 2018.

Sessions said that while the Trump administration does not want to separate children from their parents, "we cannot and will not encourage people to bring children by giving them blanket immunity from our laws."

U.N. rebuke

In a rare rebuke of the United States, United Nations Secretary-General Antonio Guterres said migrant children should not be separated from their families at the U.S.-Mexico border.

"Children must not be traumatized by being separated from their parents. Family unity must be preserved," a spokesman for Guterres said in a statement.

"This is a manufactured crisis. It is not necessary to separate parents and children to effectively enforce the nation's immigration laws," said Doris Meissner, who was commissioner of the Immigration and Naturalization Service for seven years during the Clinton administration.

"Earlier administrations have grappled with comparable issues and their responsibility for enforcing the same laws," she added. "They have made different choices on how best to enforce the laws because they have understood and recognized that the practices we are witnessing today are at odds with fundamental American values and principles."

People participate in a protest against recent U.S
People participate in a protest against recent U.S. immigration policy that separates children from their families when they enter the United States as undocumented immigrants, in front of a Homeland Security facility in Elizabeth, New Jersey, June 17, 2018.

The House of Representatives is preparing for expected votes this week on major changes to U.S. immigration laws.

Trump is scheduled to meet with House Republicans on Tuesday to discuss two competing Republican immigration reform bills.

Sanders on Monday told reporters Trump is willing to sign either bill.

Both would provide legal status to hundreds of thousands of undocumented immigrants brought to the United States as children, make sweeping changes to legal immigration, and boost U.S. border security. However, it is unclear if either will attract enough votes to pass.

"The degree to which the president seemingly believes and continues to equate immigrants and refugees with crime and danger contributes to heightening fear and opposition to immigration," Meissner told VOA. "This makes it very difficult for members of Congress to reach agreement on important legislative measures that the country should be taking to manage immigration challenges more effectively."