Attorney General Jeff Sessions slammed critics who faulted the policy for dividing families who illegally cross the US border from Mexico, adding Mr Obama was responsible, Fox News reports.
He said word got around during President Obama’s tenure that those who would illegally try and cross the border with a minor would “given immunity from prosecution”.
He added: “Word got out about this loophole, with predictable results.
“The number of aliens illegally crossing with children between our ports of entry went from 14,000 to 75,000 — that’s a five-fold increase — in just the last four years.”
The “zero tolerance” policy, which was introduced six weeks ago, has been slammed by critics including Mr Trump’s wife, Slovenian-born first lady Melania Trump, who demanded he “govern with heart” in a rare mediation.
A spokeswoman for Melania Trump said: “Mrs Trump hates to see children separated from their families and hopes both sides of the aisle can finally come together to achieve successful immigration reform.
“She believes we need to be a country that follows all laws but also a country that governs with heart.”
Under the protocol, adults are being detained and prosecuted and their children are shipped off to separate shelters in a shake-up of the past reforms, which saw many illegal immigrants allowed to remain at liberty while awaiting proceedings.
Images and videos of children in high cages, crying for their parents, with litter and tin foil used as blankets has been doing the rounds on the internet, sparking outrage.
Mr Sessions was adamant the detained kids “are not being abused” and that the Department of Health and Human Services “holds them in good conditions, they work hard at it”.
He added: “The vast majority of those children still tend to be the unaccompanied minors, but we have had a big surge in families bringing children or some adults bringing children with them.”
Mr Trump himself said he “hates to see separation of parents and children” and also pinned the blame on Democrats for pursuing a “horrible and cruel legislative agenda”.