Washington, Jun 18 (IANS): Former federal ethics chief Walter Shaub has called on US President Donald Trump to end his migrant policies at the US border, referring to them as "monstrous".

"Dry your eyes and focus. Your problems are nothing compared to the problems you're creating for the terrified children you're ripping from the arms of desperate parents at the border. This is monstrous. Stop it. Stop it now!" Shaub said in a tweet directed at Trump on Sunday.

He was referring to the administration's "zero tolerance" migrant policy at the country's border, which has resulted in the separation of families who have crossed into the US illegally.

The immigration policy and resulting separations of undocumented parents and kids is exploding into the "most emotive and politically unpredictable" test of Trump's effort to change the character of America, CNN said.

The policy charges every adult caught crossing the border illegally with federal crimes, as opposed to referring those with children mainly to immigration courts, as previous administrations did, according to media reports.

Because the US government is charging the parents in the criminal justice system, children are separated from them, without a clear procedure for their reunification aside from hotlines the parents can call to try to track down their children.

Shaub had earlier blasted Homeland Security Secretary Kirstjen Nielsen, calling her a "liar" after she defended the Trump administration's migrant policies on Twitter.

"Sorry, @SecNielsen, that was probably confusing. I don't mean to be unfair. Let me try to put it in terms you'll understand: Liar. Period," Shaub said.

Nielsen denied in a series of tweets on Sunday that the administration had a policy of separating families at the border.

Nearly 2,000 children have been separated from their parents and guardians and placed into holding facilities between April 19 and May 31 of this year, according to the Department of Homeland Security.