Washington DC - The Justice Department has launched a civil rights probe into the killing of Minneapolis protester Alex Pretti, an official said Friday, insisting the move was part of a "standard investigation."

Pretti, a 37-year-old intensive care nurse and US citizen, was shot dead on Saturday by immigration agents after they forced him to the ground in a scuffle captured on video.

The White House has sought to cool widespread outrage over the killing, though President Donald Trump on Friday renewed criticism of Pretti, describing him as an "agitator."

Deputy Attorney General Todd Blanche confirmed during a press conference Friday that the Justice Department has opened a civil rights investigation into Pretti's death.

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But he downplayed the development as normal practice.

"I don't want the takeaway to be that there's some massive civil rights investigation that's happening," he said. "This is what I would describe as a standard investigation by the FBI when there's circumstances like what we saw last Saturday.

"And that investigation, to the extent it needs to involve lawyers at the Civil Rights Division, it will involve those."

Blanche said, however, there was no civil rights probe into the death of Renee Good, another US citizen shot by an immigration agent in Minneapolis earlier in January.

"There are thousands, unfortunately, of law enforcement events every year where somebody is shot. The Civil Rights Division of the Department of Justice does not investigate every one of those shootings.

"There has to be circumstances or facts, or maybe unknown facts, but certainly circumstances that warrant an investigation," he said.