The number of migrants encountered at the border in April increased slightly compared to already high numbers encountered in March, according to Customs and Border Protection data released Tuesday -- although the number of unaccompanied minors coming across decreased.

CBP encountered 178,622 migrants trying to enter the U.S. in April, a three percent increase over the approximately 172,000 encountered in March, which was the highest number in 20 years. 

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"CBP continues to see a large influx of illegal migration along the Southwest Border," acting CBP Commissioner Troy Miller said in a statement.

The agency said that the number of unaccompanied children from Northern Triangle countries dropped by 12 percent, with 13,962 in April compared with 15,918 in March. While single adults and some family units can be quickly expelled via Title 42 health protections, the Biden administration is not expelling unaccompanied children -- which has led to a dramatic spike in the number of children in custody and one that has overwhelmed border authorities.

While the Biden administration has touted its success in relieving the pressure by emptying packed border facilities like the key site in Donna, Texas, many of those children have been moved to Health and Human Services (HHS) custody -- with numbers nearly doubling in a just a few months from just under 12,000 in March to more than 22,000 at the beginning of this month..

The number of migrant encounters showing signs of leveling off is likely to be seen as good news by the administration, but the numbers are still extremely high and may still surge as the spring and summer months arrive -- times that have typically seen increases in migrant numbers in past years. The administration has noted that the majority of those encountered are single adults, who can be removed via Title 42. In April, 111,714 migrants were expelled via Title 42.

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Critics have blamed the Biden administration’s rhetoric that they say has encouraged migration, as well as its dramatic rollback of Trump-era policies in the first days in office -- like border wall construction, increased interior enforcement and the Migrant Protection Protocols, which kept migrants in Mexico while they awaited their hearings.

The Biden administration has blamed the Trump administration for not having been prepared for such a surge and has also focused on the "root causes" of the crisis, like poverty, gang violence and economic insecurity in Central America. It has proposed a massive $4 billion investment to help solve the issues, and Vice President Kamala Harris has been put in charge of the diplomatic talks.

On Tuesday, Miller noted efforts by the Department of Homeland Security like Operation Sentinel -- a new project to crack down on transnational criminal organizations involved in smuggling migrants across the border.

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"In order to disrupt criminal organizations that have little regard for human life, CBP is leading the way alongside external law enforcement partners through Operational Sentinel. Day after day, CBP rescues migrants abandoned in harsh terrain, left for dead with no food or water. CBP is committed to enhancing the security of the U.S. border and helping save the lives of vulnerable migrants."

The increase in migrant encounters, however small, means the pressure from Republicans on the Biden administration is likely only to increase. They have slammed Harris for not visiting the border, and on Tuesday 20 Republican governors wrote to the White House calling for action.

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"The cause of the border crisis is entirely due to reckless federal policy reversals executed within your first 100 days in office," the letter says. "The rhetoric of the Biden administration and the rollback of critical agreements with our allies have led to the inhumane treatment of tens of thousands of children and undermined a fragile immigration system."