WASHINGTON (NewsNation Now) — Faced with a rising number of migrants at the southwest border and criticism from all sides, the Biden administration’s head of Homeland Security insisted Tuesday that the situation is under control as he defended a policy of allowing children crossing by themselves to remain in the country.

Homeland Security Secretary Alejandro Mayorkas conceded that a surge in the number of children, mostly from Central America, is a challenge for the Border Patrol and other agencies amid the coronavirus pandemic. But he rejected a policy under former President Donald Trump, which sent them immediately back to Mexico or other countries.

“They are vulnerable children and we have ended the prior administration’s practice of expelling them,” Mayorkas said in his most detailed statement yet on a situation at the border that he characterized as “difficult” but not the crisis that critics have portrayed.

The increasing number of migrants attempting to cross the border, which is at the highest level since spring 2019 but is on pace to rise to hit a 20-year peak, has become an early test for President Joe Biden as he seeks to break from his immediate predecessor, who waged a broad effort to significantly curtail both legal and illegal immigration.

Republicans in Congress on Monday stepped up attacks on Biden over a surge of migrants at the U.S.-Mexico border, but were criticized in turn by Democrats for their own immigration record, as well as Trump’s policies.

U.S. authorities saw a 60% increase in children crossing the southwest border alone between January and February to more than 9,400.

The overall increase is blamed on a number of factors, including the economic upheaval caused by the pandemic in Central America and two recent hurricanes in the region.

“Two damaging hurricanes that hit Honduras and swept through the region made living conditions there even worse, causing more children and families to flee,” Mayorkas said.

U.S. officials have also conceded that smugglers have likely encouraged people to try to cross under the new administration.

Some progressive Democrats and others, meanwhile, have assailed the Biden administration for holding migrant children in U.S. Customs and Border Protection detention facilities longer than the allowed 72 hours as it struggles to find space in shelters run by the Department of Health and Human Services.

On Monday, the Border Patrol encountered about 4,700 people crossing the border illegally from Mexico, including 1,575 in the Rio Grande Valley, the busiest corridor for illegal crossings, the official said. That’s up from a daily average of nearly 3,500 across the border in February and higher than about 4,300 during the peak of the Trump surge in 2019.

The overall increase is blamed on a number of factors, including the economic upheaval caused by the pandemic in Central America and two hurricanes in the region. U.S. officials have also conceded that smugglers have likely encouraged people to try to cross under the new administration.

House Minority Leader Kevin McCarthy led a delegation of a dozen Republican lawmakers on Monday to the border in Texas and blamed the Biden administration for driving an increase in migrants by actions that include supporting legislation in Congress that would provide a path to citizenship for millions of undocumented people now in the country and halting border wall construction.

“The sad part about all of this is it didn’t have to happen. This crisis was created by the presidential policies of this new administration,” McCarthy said.

Trump confronted a similar surge in 2019 even as he rushed to expand the border wall system along the border and forced people seeking asylum to do so in Central America or remain in Mexico. A year earlier he forcibly separated migrant children from their families as part of a zero-tolerance campaign that became one of the most significant political challenges of his administration.

After dropping during the start of the pandemic, the number of migrants caught while crossing the border began to rise in April. Some of the increase is due to people who are repeatedly caught after being expelled under the public health order.

The total number of people encountered by CBP rose about 28% from January to February to just over 100,000, most of whom were single adults. The last time the number was that high was in June 2019.

Mayorkas acknowledged that Border Patrol facilities are crowded and that the 72-hour time frame for their transfer to HHS is not always met.

Migrants who are under 18 years old are being allowed to remain in the country while the government decides whether they have a legal claim to residency, either under asylum law or for some other reason.

The U.S. is continuing to expel most single adults and families either to Mexico or to their countries of origin. Mayorkas said exceptions are being made for adults with “certain acute vulnerabilities” that he did not specify or for families when Mexican authorities don’t have capacity in shelters to accept them.

Mayorkas noted that 80% of the children, most of whom are from the three Northern Triangle countries of Central America, have a relative in the U.S. and 40% have a parent.

“These are children being reunited with their families who will care for them,” Mayorkas said.

The Biden administration last week ended a Trump administration policy that made relatives reluctant to contact HHS to retrieve children for fear of being deported themselves.

It has enlisted the Federal Emergency Management Agency to set up new temporary facilities to house migrant children in Texas and Arizona, working with HHS to expand shelter capacity and backing aid to Honduras, Guatemala and El Salvador to try to stem the flow of migrants at the source.

Mayorkas also criticized the previous administration for dismantling an asylum system that would have enabled a more “orderly” immigration system, cutting aid to Central America and failing to vaccinate Border Patrol agents.

“We have to rebuild the entire system, including the policies and procedures required to administer the asylum laws that Congress passed long ago,” Mayorkas said.

He promised that the U.S. has made progress in addressing the border situation.

“We have no illusions about how hard it is, and we know it will take time,” Mayorkas said. “We will get it done.”

The Associated Press, Reuters and Nexstar contributed to this report. All reporting by AP’s Ben Fox, Reuters’ Doina Chiacu and Nexstar Washington Correspondent Kellie Meyer.