A man attacked a Muslim employee at a John F. Kennedy Airport lounge in New York and shouted that U.S. President Donald Trump "will get rid of all of you," authorities said.

Meanwhile, the FBI is investigating bomb threats against a Denver community centre catering to Muslim refugees.

The incidents come to light amid heightened consternation in the Muslim-American community over an executive order signed on Friday by Trump to limit the flow of refugees from some predominantly Muslim countries into the United States.

Robin Rhodes, of Worcester, Mass., had arrived at JFK from Aruba and was awaiting a connecting flight to Massachusetts on Wednesday night when he approached Rabeeya Khan, who wears a hijab, at the Sky Club in Terminal 2 while she was sitting in the utility office, authorities said.

Khan is a contracted employee based at the Sky Club and works for a facility services company called ISS, according to Delta.

Khan told police that Rhodes came to the door and went on a profanity-laced tirade, asking her if she was praying, district attorney Richard A. Brown said. Rhodes then punched the door, which hit the back of Khan's chair, he said.

The 60-year-old Khan asked Rhodes what she had done to him and Rhodes said she'd done nothing, authorities said. He then cursed at her and kicked her in the leg, Khan told police.

When another person tried to calm him down, Rhodes moved away from the door and Khan ran out of the office to the front desk at the club, authorities said. Rhodes, 57, followed her, got down on his knees and began to bow down to imitate Muslim prayers and shouted obscenities, investigators said.

Khan recalled Rhodes saying: "Trump is here now. He will get rid of all of you. You can ask Germany, Belgium and France about these kinds of people. You see what happens," prosecutors said.

The airline called the incident "totally unacceptable."

Rhodes appeared in court Thursday night on charges of assault and menacing as hate crimes and is being held on $30,000 bail. He was represented by a public defender for the court hearing, but will have to get his own attorney for subsequent proceedings. His next court date is Feb. 8.

Bomb threats

Meanwhile in Colorado, anonymous notes threatening to "blow up" a refugee community centre catering mainly to Muslims were found at the Denver-area building, prompting a hate-crime investigation by the FBI, police said on Friday.

The two identical, typewritten notes were left on Thursday in the parking lot and stairwell of the Mango House in the Denver suburb of Aurora, both with the message: "[We're] gonna blow up all of you refugees," according to police spokesman Sgt. Chris Amsler.

These notes were found at the Mango House in Aurora, Colo. (Mango House/Facebook )

Police evacuated and checked the refugee centre in Aurora after the notes were discovered but found no signs of explosives or other suspicious devices and have not identified any suspects, Amsler told Reuters.

"This is an ongoing investigation and is a top priority for us," Amsler said. "We don't tolerate that type of thing in the city of Aurora."

The FBI office in Denver declined comment, but Amsler said, "The FBI is now assisting us in our efforts to solve this bias-motivated crime."

Dr. P.J. Parmar, a physician who runs a general medical practice inside the building that serves refugees in the Denver metropolitan area, said he treats patients from a number of war-torn countries, primarily from Africa and the Middle East.

He called the anonymous threats "unfortunate," but said, "It hasn't changed what we do, and we're still seeing patients."

The building also houses tenants who provide language and citizenship classes, a food bank and other resettlement services to political refugees.

'Now they have a voice'

A spokesman for the Washington-based Council for American-Islamic Relations (CAIR) said the threats were especially egregious for targeting a vulnerable population.

"Those fleeing violence and persecution must be welcomed and supported, not targeted by hate," Ibrahim Hooper said in a statement.

"State and federal law enforcement authorities should treat this as a terroristic threat and act accordingly."

Parmar said he believed it was no coincidence that such a threat coincided with the president's moves to curb the flow of refugees into the country.

"There's always been xenophobic element in society, but now they have a voice that allows them to come out of the shadows," he said.