Former Vice President Joe Biden on Friday laid into President Trump's "zero tolerance" immigration policy, calling the resulting separation of thousands of migrant families "one of the darkest moments in our history."

"Grotesque lies - lies about immigrants, about crime, about costs to the community. They're simply lies - factually inaccurate," Biden told a crowd in Phoenix at the national convention for the Latino civil rights organization LULAC, according to NBC News.

"And look folks, this administration's policies that literally rip babies from the arms of their mothers and fathers - one of the darkest moments in our history," Biden added.

The Trump administration has reunited 450 children between the ages of 5 and 17 with their parents one week before a court-imposed deadline. They are part of the some 2,500 children taken into U.S. custody after being separated from their families at the U.S.-Mexico border.

A federal judge who has criticized the administration's tardiness while reuniting the families offered praise during a status hearing Friday, saying "it really does appear there's been great progress" on reunifications ahead of next week's deadline.

"The reunifications are happening very rapidly, which is good. A big block will be reunified in a timely manner," U.S. District Judge Dana Sabraw said.

Trump signed an executive order last month ending his administration's controversial practice of separating children from their parents while the adults are prosecuted for illegally crossing the border.

But critics have continued to hammer the administration as it works to reunite hundreds of children with their parents.

Biden broadened his attacks on Trump during his speech to Latino activists in Arizona on Friday night, accusing the administration of an "assault on our dignity."

"It doesn't just reveal itself in the betrayal of the Dreamers or the pardoning of a sheriff who has terrorized the community," he said, according to NBC. "It is also in the underfunding of our schools, and the attacks on labor, and the ability of workers to bargain for their own worth."

Biden, who has not ruled out a 2020 presidential bid, has clashed with Trump periodically over the past couple of years and has ratcheted up his criticism of the president in recent months.

In June, he criticized the results of Trump's summit with North Korean leader Kim Jong Un and slammed Trump's controversial joint press conference with Russian President Vladimir Putin in Helsinki earlier this week, calling it "beneath the dignity" of the presidency.

Trump on Thursday told CBS News that the former vice president would be his "dream" opponent in the 2020 race.

"I dream about Biden. That's a dream," Trump said. "Look, Joe Biden ran three times. He never got more than 1 percent and President Obama took him out of the garbage heap, and everybody was shocked that he did. I'd love to have it be Biden."