Minnesota congresswoman Ilhan Omar was attacked at an event she was hosting on Tuesday, when an audience member used a syringe to spray liquid at her, Minneapolis police said.

Omar was uninjured and continued to speak. "I'm ok. I'm a survivor, so this small agitator isn't going to intimidate me from doing my work. I don't let bullies win," she later wrote on X.

Authorities have not yet identified the liquid. According to a BBC journalist in the room, it had a sour, chemical-like smell.

Anthony James Kazmierczak, 55, has been charged with third-degree assault and is being held in custody, the local sheriff's office said.

Omar, a Democrat who became in 2019 the first Somali-American to serve in the US Congress, is a fierce critic of US President Donald Trump.

She has recently targeted the president's immigration crackdown in Minnesota, during which two US citizens have been shot dead.

On Tuesday, responding to the second fatal shooting, Trump said his administration was "going to de-escalate a little bit".

During her speaking event, Omar called for the abolition of Immigration and Customs Enforcement (ICE), a major agency involved in the operation and a target of intense scrutiny for its tactics.

Trump has frequently clashed with Minnesota's Democratic officials and has often singled out Omar in particular for personal attacks.

Prior to Tuesday's attack on the congresswoman, he told an audience in Iowa that immigrants to the US "have to show that they can love our country, be proud - not like Ilhan Omar".

In the wake of the attack on Omar, the president was asked by ABC News whether he had seen the footage of the incident, and responded that he had not.

"I don't think about her. I think she's a fraud," Trump told the outlet.

During Tuesday's event, Omar said Trump's key ally Kristi Noem - whose Department of Homeland Security (DHS) oversees ICE - should "resign or face impeachment" over recent events in her state.

In January, an immigration officer fatally shot US citizen Renee Good. And on Saturday, US citizen Alex Pretti was fatally shot after being stopped by border agents, reigniting local protests as well as a nationwide public outcry.

It was after Omar's comments about Noem that she was attacked.

As he was pushed out of the room following his use of the syringe, the attacker said that Omar was "pitting us against each other". It was not immediately clear what he was referring to.

Kazmierczak was immediately arrested, and forensic work was underway at the scene, police said.