The FBI under President Barack Obama found evidence suggesting Democratic Representative Ilhan Omar entered into a sham marriage with a man suspected of being her brother, an explosive new report claims.

The Minnesota congresswoman has long faced allegations that she married British citizen Ahmed Nur Said Elmi in 2009 to help him obtain a green card - claims previously reported by the Daily Mail.

Omar has repeatedly denied the allegations, dismissing them as a right-wing conspiracy theory. President Donald Trump's administration has since launched a fresh investigation into her immigration history.

Now, The New York Times has revealed that FBI and Homeland Security agents investigated the alleged sham marriage in 2016 and uncovered some evidence suggesting fraud.

But the investigation stalled after prosecutors concluded that potential criminal charges fell outside the five-year statute of limitations.

A separate review of Omar's immigration history in 2019, during Trump's first administration, reached a different conclusion.

Three former immigration officials told The Washington Post that investigators found insufficient evidence of wrongdoing and did not identify problems with her naturalization.

That review examined several of the same allegations now under scrutiny, including questions about her marriage, her age and her father's immigration records.

Omar has firmly denied wrongdoing and dismissed the longstanding marriage claims as a conspiracy theory.

In an interview last week with MS NOW's Chris Hayes, she described the allegation that she married her brother as 'insane' and said it originated with a blog before being amplified by right-wing conspiracy theorists.

When Hayes asked whether there was any possibility that her former husband was related to her, Omar replied: 'Not to my knowledge.'

The president pounced on her response during a rally in Iowa on October 22, mocking Omar for saying she didn't know whether her former husband was related to her.

'She didn't know whether or not she married her brother. She wasn't sure,' Trump told the crowd, calling it 'one of the worst answers I think I've ever heard.'

He also demanded that Omar resign from Congress, claiming she had used a fake name to be sworn in.

Trump cited a Justice Department filing that used the name 'Ilhan Nur Said Elmi' in reference to Omar.

Investigators are also examining questions surrounding Omar's family's arrival in the United States in 1995 and whether her father, Nur Omar Mohamed, misrepresented information on immigration paperwork.

According to The Washington Post, investigators are focusing on whether Omar or her father intentionally misstated her birth date to ensure she qualified for US citizenship through her father when he became a naturalized citizen in 2000.

Authorities are also examining whether her father omitted or misrepresented information about his past military service in Somalia.

Omar was born in Somalia in 1982 and arrived in the United States with her family in 1995, when she was around 12 or 13.

The current inquiry includes questions about whether her age was accurately recorded in immigration documents, an issue that officials reviewing her file in 2019 said they could not conclusively resolve because birth records for refugees from Somalia were often unreliable.

The scrutiny also extends to her marriage history.

Public records show Omar legally married Elmi in February 2009.

The pair separated in 2011, but did not legally divorce until December 2017.   

Elmi had previously sought to move his marriage-based green card from conditional to permanent status.

According to a former immigration official cited by The Washington Post, authorities requested additional evidence because of concerns about the marriage's validity, but Elmi withdrew the application after that request.

The latest scrutiny comes weeks after federal agents searched Omar's Washington, DC, home on October 12 as part of a criminal investigation.

Agents seized her phone and passport, and authorities have issued more than a dozen grand jury subpoenas connected to the inquiry, including subpoenas to some of her relatives.

The Justice Department has not announced charges against the congresswoman in connection with the allegations.

Homeland Security Secretary Markwayne Mullin has also weighed in on the federal investigation, saying investigators were pursuing the case and indicating that it could be presented to a grand jury.

In an October 16 interview on The Charlie Kirk Show, Mullin said investigators expected to take the case to a grand jury, but his comments did not establish that Omar had committed a crime or that prosecutors had decided to charge her.

Omar has also accused the Trump administration of using the investigation to intimidate her because of her outspoken criticism of the president.

The congresswoman said she believed the search of her home was politically motivated, pointing to Trump's repeated public attacks against her.

Trump has denied involvement in the search, while administration officials have maintained that law enforcement decisions are based on the facts and the law.

The Justice Department has also sought to keep the application for the search warrant sealed while investigators review the evidence seized from Omar's home.

Prosecutors said releasing the material at this stage could jeopardize the ongoing investigation and that they had not yet decided whether to bring charges or whom to charge.

The investigation has raised questions about the timing of the search, which took place just weeks before the November 3 midterm elections.