Homeland Security Secretary Alejandro Mayorkas on Tuesday said that the U.S. is on track to encounter more migrants than it has in the last 20 years, as he defended the administration’s approach to a border surge that he described as "difficult" — but again fell short of calling it a crisis.

"The situation at the southwest border is difficult," Mayorkas said in a lengthy statement. "We are working around the clock to manage it and we will continue to do so. That is our job. We are making progress and we are executing on our plan.  It will take time and we will not waver in our commitment to succeed."

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"We will also not waver in our values and our principles as a nation," he said. "Our goal is a safe, legal, and orderly immigration system that is based on our bedrock priorities: to keep our borders secure, address the plight of children as the law requires and enable families to be together."

He spoke days after Customs and Border Protection (CBP) announced that it had encountered more than 100,000 migrants at the border in February, while numbers of child migrants in custody have also increased dramatically. The Biden administration has been moving to increase capacity of facilities to house migrants, and building a number of extra facilities — including looking at NASA sites and military bases.

On Saturday, Mayorkas announced he had directed the Federal Emergency Management Agency (FEMA) to support a "government-wide effort" to house child migrants.

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On Tuesday, Mayorkas said the U.S. has not seen these kinds of numbers in decades.

"We are on pace to encounter more individuals on the southwest border than we have in the last 20 years," he said, although he later added that the situation is "not new" and noted the U.S. has faced border spikes before.

The administration has faced criticism from Republicans, who have accused it of rhetoric and policies that have fueled what they describe as a crisis. President Biden has rolled back a number of Trump-era border protections, including the Migrant Protection Protocols (MPP), limited the illegal immigrants targeted by Immigration and Customs Enforcement (ICE) and proposed a pathway to citizenship for millions of illegal immigrants already in the U.S.

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Republicans have called for hearings into the matter, and urged the administration to change course — accusing Biden of encouraging the crisis.

But the administration has refused to do that, and has avoided calling it a crisis. Earlier this month, Mayorkas said the situation was a "challenge" but denied it was a crisis. White House press secretary Jen Psaki on Monday called it a "big problem" but again did not call it a crisis. President Biden has said there is a not a crisis at the border.

Mayorkas similarly avoided calling it a "crisis" on Tuesday. He noted that due to Trump-era Title 42 public health protections introduced amid the COVID-19 pandemic, most single adults encountered at the border are quickly sent back, either to Mexico or to their home countries.

Family units are also frequently expelled under Title 42, but he noted that sometimes that is not happening due to Mexico's refusal to take back some family units — which is causing the U.S. a significant headache.

"When Mexico's capacity is reached, we process the families and place them in immigration proceedings here in the United States," he said. "We have partnered with community-based organizations to test the family members and quarantine them as needed under COVID-19 protocols. In some locations, the processing of individuals who are part of a family unit has strained our border resources."

The Biden administration is not expelling unaccompanied children via Title 42, and are instead being passed through Border Patrol into the custody of the Department of Health and Human Services — before being sheltered until placed with a sponsor. He said in more than 80 percent of cases, the minor has a family member in the U.S.

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Mayorkas blamed poverty, violence, corruption and recent hurricanes for fueling the migrant numbers, and said things were made more complex by the pandemic – while blaming the prior administration for having "tore down the lawful pathways that had been developed for children to come to the United States in a safe, efficient and orderly way."

"As difficult as the border situation is now, we are addressing it.  We have acted and we have made progress," he said. "We have no illusions about how hard it is, and we know it will take time. We will get it done."

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The DHS secretary laid out what he called a "roadmap" for a new system that would see more facilities, testing, transport coordination, while noting other steps the administration is taking – including new agreements with Central American countries and expanding the Central American Minors program which involves minors from other countries being processed at home and brought to the U.S.

Mayorkas is scheduled to speak at a House Homeland Security Committee hearing on Wednesday. Republicans on that committee visited the border in the last few days, and renewed their calls for the administration to reverse course.

"We need to wake up. President Biden, why don’t you just admit you made a mistake with this policy and go back to the way it was and keep America safe for all of us?" Ranking Member John Katko said in a statement.