Washington (CNN) Former President Barack Obama and Vice President Joe Biden both denounced the Trump administration's "zero-tolerance" policy that is contributing to the high number of children being separated from their families by the US government once they illegally cross the border.

"Are we a nation that accepts the cruelty of ripping children from their parents' arms, or are we a nation that values families, and works to keep them together?" Trump's Democratic predecessor wrote in a Facebook post Wednesday marking World Refugee Day.

Obama argued that "to find a way to welcome the refugee and the immigrant -- to be big enough and wise enough to uphold our laws and honor our values at the same time -- is part of what makes us American."

"Whether our families crossed the Atlantic, the Pacific, or the Rio Grande, we're only here because this country welcomed them in, and taught them that to be an American is about something more than what we look like, how our last names sound, or the way we worship," Obama wrote.

Biden called for an end to family separations, saying it "is fundamentally at odds with everything this nation stands for and believes."

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