UNITED NATIONS (REUTERS) - United Nations Secretary-General Ban Ki-moon on Friday praised three young Muslims killed in North Carolina as representing the best values of global citizenship and said he was deeply moved by scenes of thousands of people mourning their deaths.

Deah Barakat, 23, a University of North Carolina dental student, his wife Yusor Abu-Salha, 21, and her sister, Razan Abu-Salha, 19, a student at North Carolina State University, were gunned down on Tuesday in Chapel Hill.

All three were involved in humanitarian aid programmes.

Police charged the couple's neighbour with murder. They say initial findings indicate a dispute over parking prompted the shooting, but they are looking into whether Hicks was motivated by hatred towards the victims because they were Muslim.

"At a time of troubling tensions stoked by those who seek to twist the teachings of faith and sow division, these three young people represented the best values of global citizenship and active community compassion to build a better world for all," UN spokesman Stephane Dujarric told reporters on Friday.

Thousands of mourners attended funeral prayers for them on Thursday.

The case has garnered international attention, prompting vigils and the hashtag #MuslimLivesMatter on social media, and raising concerns among some Muslim advocates in the United States who say they have seen an increase in threats against their communities in recent weeks.

Turkish President Tayyip Erdogan on Thursday criticised US President Barack Obama for his silence following the killings.

Barakat and Yusor Abu-Salha travelled to Turkey to help perform dental fillings and root canal work for refugees, while Razan Abu-Salha helped develop a video that was intended to spread positive messages about being Muslim-American.