Washington DC - A 35-year-old American man accused of murdering a Ukrainian refugee in a case that drew the attention of President Donald Trump has been found mentally incompetent to stand trial, US media reported Wednesday.

DeCarlos Brown Jr. is charged with stabbing to death Iryna Zarutska (23) as she rode home from work on a commuter train in Charlotte, North Carolina, last August.

WBTV and other local television stations said a state psychiatric facility had determined that Brown is "incapable to proceed" and his lawyer is asking the judge to delay his trial until his competency is restored.

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The case became a political rallying point for the US right, and Trump called Brown, who is African-American, an "animal" on his Truth Social platform.

"The ANIMAL who so violently killed the beautiful young lady from Ukraine, who came to America searching for peace and safety, should be given a 'Quick' (there is no doubt!) Trial, and only awarded THE DEATH PENALTY," Trump said. "There can be no other option,!!!"

Security camera footage of the knife assault was widely shared on right-wing outlets and social media accounts to bolster Trump's crackdown on crime.

Trump has deployed National Guard soldiers on the streets of Washington and repeatedly threatened to expand the deployments to other cities with Democratic party mayors.

Brown had multiple prior convictions, including an armed robbery that led to five years in prison.

White House spokeswoman Karoline Leavitt called him a "monster" who "should have been locked up."