Protesters in Minneapolis rally against Border Patrol chief Bovino

Protesters outside a federal courthouse in Minneapolis hit out at US Border Patrol commander Gregory Bovino.

Meanwhile, a man sprayed an unknown substance on Democratic US Representative Ilhan Omar and was tackled to the ground during a town hall in the city.

Protesters gathered outside a federal courthouse in Minneapolis to rally against US Border Patrol commander Gregory Bovino.

Bovino and a few agents are leaving the city after federal officers fatally shot two people in less than three weeks.

The Border Patrol chief led agents in Los Angeles, Chicago and New Orleans before he headed to Minnesota in December.

Trump has now dispatched border czar Tom Homan to Minnesota to take charge of Immigration and Customs Enforcement operations there.

Meanwhile, a man sprayed an unknown substance on Democratic US Representative Ilhan Omar and was tackled to the ground during a town hall in Minneapolis.

Minneapolis police said officers saw the man use a syringe to spray an unknown liquid at Omar.

They immediately arrested him and booked him at the county jail for third-degree assault.

Just before that Omar had called for the abolishment of US Immigration and Customs Enforcement and for Homeland Security Secretary Kristi Noem to resign or face impeachment.

US President Donald Trump has frequently criticised the congresswoman and has stepped up verbal attacks on her in recent months as he turned his focus on Minneapolis.

Hours before the incident, the US President criticised Omar as he spoke to a crowd in Iowa, saying his administration would only let in immigrants who "can show that they love our country."

"We need people to come in legally, but they have to show that they can love our country," said Trump. "They have to show that they're not going to blow up our shopping centres, blow up our farms, kill people. They're coming in legally, but they cannot come in unless they come in legally into our country.

"And we're letting some great people come in. They have to show that they can love our country. They have to be proud, not like Ilhan Omar."

Meanwhile, US Senate Democratic Leader Chuck Schumer called Homeland Security Secretary Kristi Noem "a liar," "vicious" and "incompetent" and appealed for her be fired after the fatal shootings of Minneapolis protesters by federal authorities.

"Kristi Noem is a liar. She's vicious. She's also incompetent," said Schumer. "Donald Trump must fire her at once before another American is killed under her watch."