BOULDER, Colo. -- Boulder police are trying to identify the four men who taunted, teased and assaulted an Asian-American man, trying to get him to say, "I love America."

The 22-year-old victim told investigators he was walking down the street with some friends at about 1 a.m Friday, singing a song from the movie "Team America," when they were confronted by four men.

The men challenged the victim, calling him "Chinaman" and asking him, "Do you think you are an American?" according to the victim's friends.

Then one of the men punched the victim in the face, pulled out a knife and held it to the victim's throat, witnesses said. The attacker then punched the victim and forced him to say that he loves America, police said. The attacker and his friends then ran off, heading north.

The assailant was described as a white man, about 19 or 20 years old, with short blond hair. He was about 5 feet 10 inches tall, and was wearing a white tanktop T-shirt and black pants.

One of the men with the attacker was described as a white man with a "very long goatee." That man was wearing a long-sleeved gray sweatshirt, the witnesses said.

If found, the men could face charges of bias-motivated assault and felony menacing. The attack occurred in the area of 10th and Marine streets.

The case remains under investigation.

Anyone with information about the crime is asked to contact Detective Kristi Peterson at 303-441-3330. Those with information who wish to remain anonymous should contact Boulder County Crime Stoppers at 1-800-222-TIPS (8477) or 1-800-444-3776.

Tips can also be submitted via the Crime Stoppers Web site at www.crimeshurt.com. Those submitting tips through Crime Stoppers that lead to the arrest and filing of charges on a suspect(s) may be eligible for a cash reward of up to $1,000 from Boulder County Crime Stoppers.