A protestor dressed as Lady Liberty carries a doll, depicting a baby of color, as demonstrators march at the 'Families Belong Together March' against the separation of children of immigrants from their families on June 14, 2018 in Los Angeles.

The events came as news stories highlighting the family separations intensified political pressure on the White House, even from some of President Donald Trump's fellow Republicans.

"This must not be who we are as a nation," said Representative Jerrold Nadler, one of seven members of Congress from New York and New Jersey who met with five detainees inside a facility in Elizabeth, New Jersey, including three who said they had young relatives removed from their care after seeking asylum at the border.

Democratic lawmakers joined protesters outside immigration detention facilities in New Jersey and Texas on Sunday for Father's Day demonstrations against the Trump administration's practice of separating children from their parents at the U.S.- Mexico border.

U.S. officials said on Friday that nearly 2,000 children were separated from adults at the border between mid-April and the end of May.

In May, U.S. Attorney General Jeff Sessions announced a "zero tolerance" policy in which all those apprehended entering the United States illegally, including those seeking asylum, would be criminally charged, which generally leads to children being separated from their parents.

Administration officials have defended the tactic as necessary to secure the border and suggested it would act as a deterrent to illegal immigration.

But the policy has drawn condemnation from medical professionals, religious leaders and immigration activists, who warn that some children could suffer lasting psychological trauma.

The children are held in government facilities, released to adult sponsors or placed in temporary foster care.

In South Texas on Sunday, several Democratic lawmakers, including Senator Jeff Merkley, visited a Border Patrol Processing Center in McAllen to call attention to the policy, while Representative Beto O'Rourke, who is running for the U.S. Senate in Texas, led a protest march to a temporary detention facility for immigrant children set up near El Paso.

O'Rourke told the demonstrators they had to bear the burden of "what we now know to be happening."

"I want that burden to be so uncomfortable for so many of us that it forces us to act, it places the public pressure on those in positions of public trust and power to do the right thing for our country," O'Rourke, who is seeking to unseat Republican Senator Ted Cruz, said to applause.

Some moderate Republicans have also called on Trump to stop the separations. Senators Susan Collins and Jeff Flake wrote to White House officials on Saturday seeking more information on

the policy.

"It is inconsistent with our American values to separate these children from their parents," Collins said on CBS' "Face the Nation" on Sunday.