US immigration agents shot and killed a U.S. citizen in Minneapolis on Saturday, officials said, sparking fierce protests and condemnations from local leaders in the second such incident this month.

The Department of Homeland Security characterised the incident as an attack, saying a Border Patrol agent fired in self-defence after a man approached with a handgun and violently resisted attempts to disarm him.

But bystander videos from the scene verified by Reuters showed the man, identified as 37-year-old Alex Pretti, holding a phone in his hand, not a gun, as he tries to help other protesters who have been pushed to the ground by agents.

As the videos begin, Pretti can be seen filming as a federal agent pushes away one woman and pushes another person to the ground. Pretti moves between the agent and the women, then raises his left arm to shield himself and turns away as the agent pepper-sprays him.

Pretti turns and tries to aid the woman who has fallen as the agent continues to spray him. As Pretti lifts up the woman, the agent pulls him off her and Pretti is forced onto his hands and knees by several agents. One of them pulls an item from Pretti’s waistband then quickly moves away from the scene.

Moments later, an officer with a handgun pointed at Pretti's back fires four shots at him in quick succession. Several more shots can then be heard as another agent appears to fire at Pretti.

The agents initially all back away from Pretti’s body on the road. Some agents then seem to offer medical assistance to Pretti as he lies on the ground, as other agents keep bystanders back.

The shooting of Pretti, an intensive care nurse, drew hundreds of protesters to the neighbourhood to confront the armed and masked agents, who deployed tear gas and flashbang grenades. Demonstrations also broke out in New York, Washington D.C. and San Francisco, among other cities.

It also raised tensions between state and federal officials, already at odds with the Trump administration over the shooting of another US citizen, Renee Good, on January 7.

They have refused to allow local officials to participate in their investigation of the incident.

Police say man was lawful gun owner

Homeland Security Secretary Kristi Noem told reporters the man killed on Saturday had attacked agents on an immigration raid, though she did not say whether he pulled out his weapon. Federal officials posted an image of the gun they say Pretti was carrying at the time of the shooting.

"He wasn't there to peacefully protest. He was there to perpetuate violence," Noem said at a news conference.

Local leaders, including Minnesota Governor Tim Walz, questioned that account.

"I've seen the video from several angles and it's sickening," Walz said. "The federal government cannot be trusted to lead this investigation - the state will handle it."

The head of the Minnesota Bureau of Criminal Apprehension, Drew Evans, told reporters that federal agents blocked his team's attempts to begin an investigation on Saturday.

Minneapolis Police Chief Brian O'Hara said the man who was killed was a lawful gun owner with no criminal record other than traffic violations.

As people protested the shooting, city police and state troopers arrived to manage the crowd. The situation appeared to have calmed later Saturday after federal agents left the area, though protesters remained on the streets for hours afterward.

Local officials pleaded for restraint. "Please do not destroy our city," O'Hara said.

The nearby Minneapolis Institute of Art said it had closed for the day due to safety concerns, and the National Basketball Association postponed a Minnesota Timberwolves game.

Mayor, governor call for operation to end

Walz and other local and state officials called for an immediate end to the Trump administration's local immigration enforcement operations.

"How many more residents, how many more Americans need to die or get badly hurt for this operation to end?" Minneapolis Mayor Jacob Frey said at a press conference.

Trump accused local elected officials of stirring up opposition.

"The Mayor and the Governor are inciting Insurrection, with their pompous, dangerous, and arrogant rhetoric," the Republican president wrote on social media.

Vice President JD Vance, who visited the city on Thursday, accused local leaders of refusing to provide local police support to immigration agents. That drew a fierce response from Walz, who said the immigration crackdown has strained local police resources.

The shooting came one day after more than 10,000 people took to the frigid streets to protest the crackdown.