Ilhan Omar’s attorneys have asked the US Department of Justice to return property that federal agents removed days earlier from her home during a search.

The lawyers for the Minnesota Democrat contended that the seizure as “neither justified nor lawful”, according to a letter that the Associated Press reported on Friday.

The federal investigation into Omar was launched just weeks ahead of the 3 November midterms, in which Omar is on the ballot. Democrats accused Donald Trump, a Republican, of abusing his power as president to target a political opponent.

Omar’s attorneys wrote that there is “no legitimate basis for any suggestion that she has violated any law concerning her citizenship status”, according to the Wall Street Journal, which first reported on the lawyers’ letter.

“This vindictive, retributive, and politically motivated criminal investigation into one of the president’s chief congressional critics violates Representative Omar’s constitutional rights and threatens the separation of powers,” the congresswoman’s attorneys wrote.

The federal government has issued more than a dozen grand jury subpoenas, including of Omar’s relatives, and seized her phone in its investigation of the congresswoman.

A justice department spokesperson said the letter from Omar’s defense team was “riddled with false allegations and inaccuracies”, according to the AP.

“Our attorneys and law enforcement partners complied with all court orders and legal obligations, as they always do,” the spokesperson, Emily Covington, wrote in a text message on Friday evening.

The letter from Omar’s lawyers also accused the justice department of violating the agency’s longstanding policy aimed at avoiding potentially influencing an election. And they raised concerns about whether the investigators followed instructions from the magistrate judge who approved the search.

The attorneys demanded in the letter that the justice department preserve any audio and video taken during the search on Monday.

The justice department launched the investigation after years of Trump and conservative media figures promoting unsubstantiated rumors that Omar’s ex-husband is actually her brother – and that she married him so that he could obtain immigration status.

Omar, the most prominent Somali American in the US, has denied that allegation.

Citing sources “close to the investigation”, Fox News reported that the search on Monday was related to a criminal fraud investigation concerning Omar’s immigration paperwork. Omar’s father filled out that paperwork when she was a child.

“I’m ok,” Omar posted on X after the raid. “Make no mistake: this is an attempt to target political enemies and weaponize federal law enforcement.”

Omar also said the search was “just the latest escalation in his campaign of political intimidation”.

The president has consistently launched racist attacks against Omar and other Somali Americans in Minnesota.

In December, he described them as “garbage” who “come from hell, and they complain, and do nothing but bitch”.

He said Omar “should be thrown the hell out of our country”.

After Monday’s search, Trump denied being involved in the investigation.

“I’ve always found her to be totally crooked, personally, but that has nothing to do with me,” Trump said.

The Associated Press contributed reporting