Minneapolis, Minnesota - A US District Court has filed charges against a man accused of attacking Democratic Congresswoman Ilhan Omar during a townhall event in Minnesota, court documents show.

The criminal complaint, dated Wednesday, states that suspect Anthony Kazmierczak (55) forcibly assaulted and interfered with a US representative who was carrying out official duties, a federal offense.

"Assaultive behavior and acts of intimidation directed at officers and employees of the United States will not be tolerated," US Attorney Daniel Rosen said in a Justice Department press release. "Persons who engage in this criminal conduct can expect a swift response from law enforcement and federal prosecutors."

A supporting affidavit says that the liquid sprayed at Omar from a syringe was likely apple cider vinegar mixed with water, and that years ago, the suspect told a close associate that "someone should kill" her, referring to Omar.

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Kazmierczak rushed at the Somali-American lawmaker – a frequent target of racist attacks by President Donald Trump – on Tuesday evening as she was denouncing anti-immigrant raids in Minnesota and calling for Homeland Security chief Kristi Noem to resign.

He was immediately tackled by security guards and arrested shortly afterward. He has since been taken into custody.

Kazmierczak has a criminal record, including for drunk driving, and his social media posts express fervent support for Trump. The Republican, meanwhile, baselessly suggested the assault was staged by Omar herself.

The attack took place three days after federal agents killed a second US citizen in Minneapolis this month, sparking outrage around the country.