A 55-year-old New York man has been arrested and charged with threatening to assault and murder Democratic Representative Ilhan Omar, a Muslim US Congress member from Minnesota, federal prosecutors said.

Patrick Carlineo Jr of Addison, New York, faces up to 10 years in prison and a $250,000 fine if convicted, the US Department of Justice said on Friday in a statement.

According to prosecutors, Carlineo spoke by telephone with one of Omar's staff members on March 21 and asked the employee: "Do you work for the Muslim Brotherhood? Why are you working for her, she's a (expletive) terrorist. I'll put a bullet in her (expletive) skull."

The threat was referred to the US Capitol Police, which launched a probe in coordination with the FBI, the Justice Department said.

Carlineo sounded angry during the phone call but also spelled his name for the staff member and provided contact details, according to an affidavit by an FBI special agent.

Interviewed at his home by investigators, Carlineo "stated that he was a patriot, that he loves the President, and that he hates radical Muslims in our government," the affidavit said.

Carlineo made an initial court appearance on Friday and is being held pending a detention hearing on April 10.

Representatives of Omar, a member of the House Foreign Affairs Committee who was elected in November as one of the two first Muslim women to win seats in Congress, did not immediately respond to a request for comment.

In February, Omar apologized "unequivocally" after Republicans and Democrats condemned comments she made about the pro-Israel lobby in the United States as using anti-Semitic stereotypes. President Donald Trump said her apology was inadequate and she should be "ashamed of herself."