(Reuters) - U.S. Department of Homeland Security Secretary Kirstjen Nielsen on Wednesday defended the government’s position that the country faces a dire crisis due to migration at the U.S.-Mexico border in the face of fiery questioning from Democrats in Congress.

Testifying before Congress for the first time since Democrats took control of the House of Representatives in January, Nielsen defended President Donald Trump’s decision to declare a national emergency to unlock funding for a wall on the U.S.-Mexico border. She also repeated previous calls for Congress to lift limits on how long families can be kept in immigration detention.

“Illegal immigration is simply spiraling out of control,” Nielsen told the House Homeland Security Committee.

Democrats questioned Nielsen over the Trump administration’s “zero tolerance” prosecution policy, which last year led to the separation of thousands of migrant children from their parents and generated a fierce backlash, as well as the administration’s new restrictions on people seeking asylum at the border.

Democratic Representative Nanette Barragán challenged Nielsen over claims that the government is not turning away people seeking asylum at official ports of entry, stating that she herself on Saturday witnessed a Honduran asylum seeker being turned away by a border agent.

“Madam Secretary, I don’t know if you know what’s happening, or if this is happening without you knowing, but it’s totally unacceptable,” Barragán said.

Also on Wednesday, U.S. Customs and Border Protection Commissioner Kevin McAleenan testified before the Senate Judiciary Committee about record numbers of families from Central America crossing the border, which he said is stretching the resources and capabilities of border officials.

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New government statistics show a significant spike in arrests of migrants trying to cross the U.S. southern border: over 268,000 between October and February, a 97 percent increase over the 136,000 arrested over the same period last year, and the largest number in 12 years.

McAleenan said his agency continues to see increasing numbers of children and families from Central America, outpacing the number of single adults illegally crossing from Mexico. In February 2019, unaccompanied children and people traveling in families accounted for 65 percent of all arrests along the southwest border, according to CBP data.

McAleenan testified that human smugglers have developed new routes to take busloads of families, mostly from Guatemala, to the U.S.-Mexico border in a matter of days where large groups are then dropped off in remote areas away from infrastructure and facilities.

Border officials said they are seeing an alarming number of large groups of over 100 migrants presenting themselves at the border - 70 so far in the 2019 fiscal year, compared with 13 in all of 2018 and just two in 2017.

McAleenan said because the bulk of those detained at the border turn themselves in to authorities, a physical barrier would not have as much impact as changes to existing immigration laws that the Trump administration says incentivizes people to come with their children.