Omar’s communications director, Jacklyn Rogers, called Monday morning’s raid “an outrageous abuse of power” by the Trump administration, and said the congresswoman “has done nothing wrong”.
The nature of the criminal investigation remains unclear.
An ally of Omar gave an update to the BBC World Service’s Newsday programme. Asma Mohammed said: “She is doing well, she’s let everyone know that she’s okay and that she is used to attacks from the president but this is a new low from him.”
During Monday’s search, a BBC crew saw several agents at Omar’s home, some carrying boxes to a van.
News of the search was first reported by Fox News, which said the investigation was about immigration paperwork filed by her late father when Omar was a child.
The timing of the raid – 22 days before the November midterm elections, which will decide the balance of power in Congress for the next two years – raised concerns from Omar’s fellow Democrats.
The justice department has a longstanding policy of refraining from most enforcement action that is “likely to raise an issue or the perception” it is being brought for the purpose of affecting any election or to disadvantage a candidate.
Leading Democrats in the House of Representatives said in a statement that Omar had long been targeted with “vile personal attacks and baseless accusations” by Trump.
“Now, less than 30 days until the midterm election, his violent mass deportation machine has descended upon the home of a duly elected Member of Congress and her family,” they said.
Omar’s immigration records have been scrutinised in the past by Republicans and earlier this year, a fellow congresswoman, Nancy Mace of South Carolina, unsuccessfully sought a subpoena for her records.
Last month, Homeland Security Secretary Markwayne Mullin told a conservative podcaster “something is going to happen”, and made allegations of marital fraud against Omar.
Separately, the White House’s border tsar, Tom Homan, told Fox News that Omar was being investigated for unspecified immigration violations.
Omar denied these allegations last month.
“I will say it again so it’s as clear as possible: I’m not at all worried about these investigations, because they are complete shams,” she said in a campaign fundraising email.
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