Alina Habba, US President Donald Trump's former personal lawyer, has resigned as New Jersey's top prosecutor after a court battle over her eligibility to serve as US attorney for the state.

US Attorney General Pam Bondi accepted Habba's resignation on Monday, saying the court's "flawed" ruling made it "untenable for her to run her office effectively".

Habba's exit comes a week after a US appeals court found that she had been unlawfully serving as US attorney - a ruling likely to affect scores of criminal cases in the Garden State.

Bondi said Habba will remain at the justice department as a senior adviser and will seek further review of the decision, with hopes of reversal.

Trump selected Habba for the role of US attorney this year, but after a district court rejected her nomination, the Trump administration installed her in a role that allowed her to fill in on an acting basis.

The appellate judges last week said the temporary posting, which bypassed confirmation by the US Senate, violated the Federal Vacancies Reform Act.

In a statement posted to X, Habba said she decided to step down "to protect the stability and integrity of the office which I love" in light of the court's ruling.

"But do not mistake compliance for surrender," she wrote, saying she will work as an adviser to Bondi for US attorneys. "My fight will now stretch across the country."

Bondi wrote on X that the judges "should not be able to countermand the President's choice of attorneys entrusted with carrying out the executive branch's core responsibility of prosecuting crime".

The attorney general praised Habba's record and said that during her run, the state capital of Newark saw a 20% reduction in crime and that the city of Camden experienced its first summer in 50 years without a homicide.

Habba, 41, first joined Trump's personal legal team in 2021 after reportedly meeting him at his golf club in Bedminster, New Jersey.

She went on to represent Trump in his hush-money trial in New York last year, when he was convicted on 34 counts of falsifying business records. Trump has filed an appeal against that conviction.

Before Habba took on the role of US attorney for New Jersey, Trump had announced he was appointing her as his presidential counsellor during his second administration, describing Habba as "unwavering in her loyalty" and a "tireless advocate for justice".

Several other US attorneys appointed by Trump have been found to be serving unlawfully, primarily because their appointments circumvent confirmation by the Senate - the arm of the legislative branch of US government that traditionally appoints US attorneys.

At the White House on Monday, Trump echoed Habba and Bondi's frustration with the "blue slip" - a process that allows home-state senators to signal whether they approval or disapprove of judicial nominees that was originally intended as a courtesy to ensure presidential collaboration.

"I can't appoint a US attorney that's not a Democrat," he said. "What it means is, I guess I just have to keep appointing people for three months and then just appoint another one, another one. And it's a very sad situation. We're losing tremendous, we're losing a lot of great people."

He said that seven attorneys will not be able to be US attorneys because of the blue slip.

Last month, another of Trump's personal lawyers, Lindsey Halligan, was disqualified from her post in Virginia because her appointment violated the statute governing interim US attorneys.

A federal judge in California also ruled in October that acting US attorney Bill Essayli had been serving unlawfully in the Central District of California.

In September, a Nevada judge issued a similar opinion regarding Sigal Chattah in that state, but paused her disqualification pending appeal.