Washington, Dec 12 (AP) Homeland Security Secretary Kristi Noem defiantly defended the Trump administration's hard-line immigration policies on Thursday during a House committee hearing, portraying migrants as a major threat faced by the nation that justifies a crackdown that has seen widespread arrests, deportations and a dizzying pace of restrictions on foreigners.

Noem, who heads the agency central to President Donald Trump's approach to immigration, received backup from Republicans on the panel but faced fierce questioning from Democrats, including many who called for her resignation over the mass deportation agenda.

The secretary's testimony was immediately interrupted by protesters shouting for her to stop Immigration and Customs Enforcement raids and "end deportations." They trailed her down the halls as she left early for another engagement, chanting, "Shame on you!" But she vowed she "would not back down." "What keeps me up at night is that we don't necessarily know all of the people that are in this country, who they are and what their intentions are," Noem said.

The hearing was Noem's first public appearance before Congress in months, testifying at the House Committee on Homeland Security on "Worldwide Threats to the Homeland," and it quickly grew heated as she emphasised how big a role she believed immigration played in those threats. It focused heavily on the Trump administration's immigration policies, whereas in years past the hearing has centred on issues such as cybersecurity, terrorism, China and border security.

Rep Bennie Thompson, the panel's ranking Democrat, said Noem has diverted vast taxpayer resources to carry out Trump's "extreme" immigration agenda and failed to provide basic responses as Congress conducts its oversight.

"I call on you to resign," the Mississippi congressman said. "Do a real service to the country." Trump returned to power with what the president says is a mandate to reshape immigration in the US. In the months since, the number of people in immigration detention has skyrocketed; the administration has continued to remove migrants to countries they are not from; and, in the wake of an Afghan national being accused of shooting two National Guard troops, Noem's department has dramatically stepped up checks and screening of immigrants in the US.

Tough questions from Democrats Several Democrats repeatedly told Noem flatly that she was "lying" to them and to the public over claims they are focused on violent criminals. They presented cases of US citizens being detained in immigration operations and families of American military veterans being torn apart by deportations of loved ones who have not committed serious crimes or other violations.

"You lie with impunity," said Rep Delia Rodriguez, D-Ill, who said Noem should resign or be impeached.

Republicans largely thanked Noem for the work the department is doing to keep the country safe and urged her to carry on.

"Deport them all," said Rep Andy Ogles, R-Tenn.

Since Noem's last Congressional appearance in May, immigration enforcement operations, especially in Los Angeles and Chicago, have become increasingly contentious, with federal agents and activists frequently clashing over her department's tactics.

Noem did not address the calls to resign, but she tangled with the Democratic lawmakers -- interrupting some -- and suggested that she and the department she leads were not going anywhere.

"We will never yield. We will never waver," she said.

Noem, whose own family, including an infant granddaughter, was in the audience, praised the Trump administration's efforts when it comes to immigration, saying, "We're ending illegal immigration, returning sanity to our immigration system." During the hearing, a federal judge ordered the government to free Kilmar Abrego Garcia, whose wrongful deportation to a notorious prison in El Salvador made him a flashpoint in the Trump administration's immigration enforcement. Noem did not address the judge's order, nor was she asked about it during the hearing.

Noem left early, saying she was headed to a meeting of the Federal Emergency Management Agency review council. The meeting, however, was abruptly canceled with no reason given. (AP) RUK RUK