Washington (CNN) Acting Homeland Security Secretary Kevin McAleenan on Sunday said 350 migrant children remain in US Customs and Border Protection custody -- down from 2,500 last month -- after Congress passed a $4.6 billion border funding bill allowing CBP to shift more children into the Department of Health and Human Services' shelter system.

"On June 1 we have 2,500 children in our custody; 1,200 had been with us over three days. Now that we have the supplemental from Congress, HHS has additional beds. We only have 350 after yesterday afternoon's report and only 20 of those children have been with us more than three days so that's a huge improvement based on the resources we asked for from Congress and were finally given," McAleenan said on ABC's "This Week."

McAleenan was also asked about the discovery of a second CPB-connected secret Facebook group that featured mocking images and vulgar and sexually explicit posts

The roughly 1,000-member group -- called "The Real CBP Nation" -- was found to host to an image that mocks separating migrant families , multiple demeaning images of New York Democratic Rep. Alexandria Ocasio-Cortez and other mocking photos of minorities.

McAleenan said Sunday he wasn't previously aware of the group, but that he was "made aware that we had an allegation in 2016 that was investigated, followed up on and discipline was metered out." He said that "several agents" have been placed on "administrative duties" and that an investigation is ongoing.

"This investigation is continuing and the agents will be held accountable if they're CBP employees who did inappropriate things," he said. "I don't think it's reflective of the men and women we have."

When asked about immigration raids by ICE -- an operation that President Donald Trump said his administration would launch sometime after the Fourth of July , McAleenan said they were part of a "balance enforcement process."

"You can't do this all at the border. That's why I've been going down to Central America to work on the origins of this crisis and address the human smugglers that are incentivizing and inviting people into this dangerous cycle in the first place," McAleenan said. "That's why we're enhancing our border security, that's why we've asked Congress to change the laws, but it's also why we need to do interior enforcement."