The FBI on Friday arrested a judge whom the agency accused of obstruction after it said she helped a man evade US immigration authorities as they were seeking to arrest him at her courthouse.

The county circuit judge, Hannah Dugan, was apprehended in the courthouse where she works in Milwaukee, Wisconsin, at 8.30am local time on Friday on charges of obstruction, a spokesperson for the US Marshals Service confirmed to the Guardian.

Kash Patel, the Trump-appointed FBI director, wrote mid-morning on X: “We believe Judge Dugan intentionally misdirected federal agents away from the subject to be arrested in her courthouse, Eduardo Flores Ruiz, allowing the subject – an illegal alien – to evade arrest.”

He said that agents were still able to arrest the target after he was “chased down” and that he was in custody. Patel added that “the judge’s obstruction created increased danger to the public”. The FBI director deleted the post minutes later for unknown reasons, but the US marshals confirmed to multiple outlets that the arrest had occurred.

Dugan appeared briefly in federal court in Milwaukee later on Friday morning before being released from custody. Her next court appearance is 15 May.

“Judge Dugan wholeheartedly regrets and protests her arrest. It was not made in the interest of public safety,” her attorney, Craig Mastantuono, said during the hearing. He declined to comment to an Associated Press reporter, following her court appearance.

A crowd formed outside the courthouse, chanting: “Free the judge now.”

In a statement shared with the Milwaukee Journal Sentinel, an attorney for Dugan said: “Hannah C Dugan has committed herself to the rule of law and the principles of due process for her entire career as a lawyer and a judge.”

It continued: “Judge Dugan will defend herself vigorously, and looks forward to being exonerated.”

Trump weighed in on his Truth Social platform by sharing an image of the judge taken from her campaign’s Facebook page in which she was seen on the bench wearing a KN95 face mask and displaying the Ukrainian national symbol of a trident. The image was first posted on X by the rightwing blogger Libs of TikTok.

The Milwaukee city council released a statement following the arrest: “This morning’s news that Judge Hannah Dugan was arrested by federal authorities is shocking and upsetting. Judge Dugan should be afforded the same respect and due process that she has diligently provided others throughout her career.

“Perhaps the most chilling part of Judge Dugan’s arrest is the continued aggression by which the current administration in Washington, DC has weaponized federal law enforcement, such as ICE, against immigrant communities,” the statement reads. “As local elected officials, we are working daily to support our constituents who grow increasingly concerned and worried with each passing incident.”

Senator Tammy Baldwin, a Democrat representing Wisconsin, called the arrest of a sitting judge a “gravely serious and drastic move” that “threatens to breach” the separation of power between the executive and judicial branches.

“Make no mistake, we do not have kings in this country and we are a democracy governed by laws that everyone must abide by,” Baldwin said in an emailed statement after Dugan’s arrest.

The leftwing senator Bernie Sanders said the move was about “unchecked power”.

“Let’s be clear. Trump’s arrest of Judge Dugan in Milwaukee has nothing to do with immigration. It has everything to do with [Trump] moving this country towards authoritarianism,” he said in a statement.

The Massachusetts senator Elizabeth Warren said in a social media post: “This administration is threatening our country’s judicial system. This rings serious alarm bells.”

The judge’s arrest dramatically escalates tensions between federal authorities and state and local officials amid Donald Trump’s anti-immigration crackdown. It also comes amid a growing battle between the Trump administration and the federal judiciary over the president’s executive actions over deportations and other matters.

In a statement Wisconsin’s governor, Democrat Tony Evers, accused the Trump administration of repeatedly using “dangerous rhetoric to attack and attempt to undermine our judiciary at every level”.

“I have deep respect for the rule of law, our nation’s judiciary, the importance of judges making decisions impartially without fear or favor, and the efforts of law enforcement to hold people accountable if they commit a crime,” Evers said. “I will continue to put my faith in our justice system as this situation plays out in the court of law.”

It was reported on Tuesday that the FBI was investigating whether Dugan “tried to help an undocumented immigrant avoid arrest when that person was scheduled to appear in her courtroom last week”, per an email obtained by the Milwaukee Journal Sentinel.

Dugan told the Journal Sentinel: “Nearly every fact regarding the ‘tips’ in your email is inaccurate.”

The arrest of Dugan is the first publicly known instance of the Trump administration charging a local official for allegedly interfering with immigration enforcement.

Emil Bove, the justice department’s principal associate deputy attorney general, issued a memo in January calling on prosecutors to pursue criminal cases against local government officials who obstructed the federal government’s immigration enforcement efforts.

Bove stated in the three-page memo: “Federal law prohibits state and local actors from resisting, obstructing, and otherwise failing to comply with lawful immigration-related commands or requests.”

Dugan has been charged with the federal offenses of obstructing a proceeding and concealing an individual to prevent arrest, according to documents filed with the court.

The administration alleged that in the original encounter, the judge ordered immigration officials to leave the courthouse, saying they did not have a warrant signed by a judge to apprehend the suspect they were seeking, who was in court for other reasons.

Prosecutors said that Dugan became “visibly angry” when she learned that immigration agents were planning an arrest in her courtroom, according to court filings.

Dugan ordered the immigration officials to speak with the chief judge and then escorted Flores Ruiz and his attorney through a door that led to a non-public area of the courthouse, the prosecution complaint said.

The Milwaukee Journal-Sentinel, citing sources it did not identify, said Dugan steered Flores Ruiz and his attorney to a private hallway and into a public area but did not hide the pair in a jury deliberation room as some have accused her of doing.

Dugan was first elected as a county judge in 2016 and before that was head of the local branch of Catholic Charities, which provides refugee resettlement programs. She was previously a lawyer at the Legal Aid Society of Milwaukee, which serves low-income people.

The case is similar to one brought during the first Trump administration against a Massachusetts judge, who was accused of helping a man sneak out a backdoor of a courthouse to evade a waiting immigration enforcement agent.

That prosecution sparked outrage from many in the legal community, who slammed the case as politically motivated. Prosecutors under the Biden administration dropped the case against Newton district judge Shelley Joseph in 2022 after she agreed to refer herself to a state agency that investigates allegations of misconduct by members of the bench.

The Associated Press contributed reporting