US President Barack Obama has described the deaths of three young Muslims gunned down in North Carolina as "brutal and outrageous murders", and said no one in the US should be targeted for their religion.

The president's statement came as the US Justice Department said it would join the FBI's preliminary inquiry to determine whether the man accused in the Chapel Hill shooting on Tuesday broke any federal laws, including hate crime laws.

"No one in the United States of America should ever be targeted because of who they are, what they look like, or how they worship," Mr Obama said in a statement, offering his condolences to the victims' families.

The families had called on the president to insist federal authorities investigate whether the murder suspect, 46-year-old paralegal student Craig Stephen Hicks, was motivated by hatred toward the victims because they were Muslim.

Newlywed Deah Shaddy Barakat, 23, a University of North Carolina dental student, his wife Yusor Mohammad Abu-Salha, 21,and her sister, Razan Mohammad Abu-Salha, 19, a student at North Carolina State University, were killed in a condominium about 3km from the UNC campus.

On Thursday, Turkish President Tayyip Erdogan criticised Mr Obama and other US leaders for their silence about incident, which has garnered international attention and left some US Muslims feeling concerned about their safety.

United Nations Secretary-General Ban Ki-moon praised the three victims, who were all involved in humanitarian aid work, as representing the best values of global citizenship and said he was deeply moved by scenes of thousands of people mourning their deaths.

A Justice Department spokeswoman said its Civil Rights Division and the US Attorney's Office for the Middle District of North Carolina would participate in the FBI inquiry announced in the case.

In a separate investigation local police cited a parking dispute as Mr Hicks' motive, but said they were also looking into whether religious hatred played a role.

Neighbours said Mr Hicks, who posted anti-religion messages and a photo of a gun he said belonged to him on his Facebook page, was known in the community as someone prone to grow angry over parking troubles and noise.

Mohammad Abu-Salha, the father of the two female victims, told CNN that his daughter Yusor had said Mr Hicks made her feel uncomfortable after she moved into a neighbouring condo where her new husband lived.

"Daddy, I think he hates us for who we are," Abu-Salha said his daughter told him, according to CNN.