Washington DC - Department of Homeland Security chief Kristi Noem came under withering criticism from Democratic lawmakers on Tuesday over the Trump administration's sweeping immigration crackdown.

"Under your leadership, the Homeland Security Department has been devoid of any moral compass or respect for the rule of law," Senator Dick Durbin, a Democrat from Illinois, told Noem at a Senate Judiciary Committee oversight hearing.

"DHS agents have wreaked havoc in our cities," Durbin said. "They roam the streets in paramilitary gear and arrest and detain people based on the color of their skin, their accents, and the language they speak."

Immigration agents shot dead two Americans during protests in Minnesota recently and Noem leveled "baseless accusations of domestic terrorism" against them following their deaths, Durbin said.

Noem, making her first appearance before Congress since the shootings, expressed her condolences to the families over the "tragic" deaths of Renee Good and Alex Pretti in Minneapolis and claimed she did not call them domestic terrorists.

"I said it appeared to be an incident of [domestic terrorism]," she said.

Republican President Donald Trump campaigned for the White House on a pledge to deport millions of undocumented migrants, and Noem, as head of DHS, is the chief enforcer of that policy.

Noem defended the department's actions, saying US-Mexico border crossings have plummeted to historic lows and that "nearly three million" undocumented migrants have been removed from the US during the past year.

"Our department has delivered historic results and has made our community safer since the start of President Trump's second term," she said.

Democratic Senator Chris Coons accused DHS of acting unconstitutionally in a bid to meet White House demands for "higher and higher numbers for deportations."

"It's why we have roving patrols, racially profiling whomever they see and creating a 'show me your paper state,'" Coons said.

"It's why you go into sensitive locations like churches, hospitals, and schools. It's why you have been arresting children, the elderly, refugees, the disabled," he said.

Noem denied DHS was operating under a quota system.

"There are no quotas at the Department of Homeland Security," she said. "When we do law enforcement operations, we do them on targeted enforcement, getting public safety threats off of our streets and out of our communities to protect the American people."

Noem also urged lawmakers to reach an agreement ending a partial government shutdown that has choked off funding for parts of her department.

Thousands of government workers, from airport security agents to disaster relief officials, are being furloughed or forced to work without pay until funding is agreed upon by Congress.

Democrats oppose any new funding for DHS until major changes are implemented in how the Immigration and Customs Enforcement agency conducts its operations.

They have demanded curtailed patrols, a ban on ICE agents wearing face masks, and a requirement that they obtain a judicial warrant before entering private property.