New York City police are investigating reports a man wearing a traditional south Asian outfit was beaten up by a pair of teenagers, who yelled "Isis, Isis" while they attacked him.

The 43-year-old victim of Bangladeshi descent, Mujibur Rahman, who was wearing a shalwar kameez, was walking his with his nine-year-old niece in the Bronx on 15 January when he was assaulted.

Police said two teenagers punched him several times in the head, knocked him down and kicked him, Reuters reported. The victim suffered bruises on his head and face although his niece was not injured.

According to Newsday, a NYPD spokesman said that no arrests have been made in the case and the investigation is "ongoing."

The Council on American Islamic Relations (CAIR) called on the Federal Bureau of Investigation (FBI) to join the investigation headed the NYPD's Hate Crime Task Force.

"The FBI should add its resources to the investigation of this disturbing incident in order to send a clear message to bigots that attacks on American Muslims will not be tolerated and that perpetrators of such attacks will face the full weight of the law," said Sadyia Khalique, the director of CAIR-NY, in a statement.

Bronx Borough President Ruben Diaz Jr condemned the attacks as "hateful" and "not representative of the shared values of the people of this borough." In a statement, Diaz Jr said, "An attack on one of us over race, religion, gender, or sexual orientation is an attack on us all."

The Washington Post noted that Muslim centres of worship across the US have become the targets of hate crimes and vandalism in recent months.

At least four incidents, including two in California, one in Florida and one in Georgia, occurred in December. The attacks are believed to be connected to fears of terrorism after the attacks in San Bernardino, California.