GENEVA/ELIZABETH, New Jersey－The UN human rights chief on Monday urged Washington to stop separating migrant children from their parents at the US border, describing the policy as "unconscionable".

"The thought that any state would seek to deter parents by inflicting such abuse on children is unconscionable," Zeid Ra'ad Al Hussein said at a session of the UN Human Rights Council in Geneva.

The "zero-tolerance" border security policy implemented by US President Donald Trump's administration has sparked global outrage.

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

"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.

The events came as news stories highlighting the family separations intensified political pressure on the White House.

US 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, US Attorney General Jeff Sessions announced the "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.

'Stop lying'

Trump has sought to blame Democrats, saying their support for passage of a broader immigration bill would end the separations.

White House adviser Kellyanne Conway said on NBC's Meet the Press on Sunday: "As a mother, as a Catholic, as somebody who has got a conscience, ... I will tell you that nobody likes this policy."

"You saw the president (say) on camera that he wants this to end," she added.

A spokeswoman for Melania Trump told CNN on Sunday that the first lady "hates to see children separated from their families" and hopes lawmakers from both parties can agree on immigration reform.

In an opinion piece in The Washington Post, former first lady Laura Bush, wife of the previous Republican president, George W. Bush, said she lives in a border state and appreciates the need to enforce and protect the US borders.

"But this zero-tolerance policy is cruel. It is immoral. And it breaks my heart," Bush wrote, adding the images were "eerily reminiscent of the Japanese-American internment camps of World War II, now considered to have been one of the most shameful episodes in US history".

Democrats have accused the president of effectively turning the children into political hostages to secure stricter immigration measures, such as funding for a US-Mexico border wall.

"Stop lying to the American people. This is your policy," Democratic US Representative Hakeem Jeffries said in New Jersey.

Reuters-AP-AFP