In this image of a courtroom sketch, Canadian defendant Omar Khadr sits with his defence team during a hearing inside the courthouse for the U.S. war crimes commission at the Guantanamo Bay U.S. naval base in Cuba on June 1, 2009. (Janet Hamlin/Reuters)

A top UN official says the United States is leery of freeing Canadian Omar Khadr from Guantanamo Bay for fear he will return to al-Qaeda once he is released.

Radhika Coomaraswamy, the United Nations' Special Representative for Children in Armed Conflict, has been meeting with the top-level White House committee reviewing the Toronto-born Khadr's file.

She said on Wednesday that of all the cases involving detainees remaining at the U.S. prison camp in Cuba, Khadr's file is the most troubling for the U.S.

"The issue is Mr. Khadr's family is quite closely linked to al-Qaeda, many of them in Pakistan, and there is this fear he will go back to that," said Coomaraswamy.

Khadr, now 22, is accused by the United States of killing a U.S. soldier with a hand grenade in Afghanistan in 2002, when he was 15. He has been held at Guantanamo Bay since then.

Pentagon prosecutors have suffered several setbacks in the case, including the revelation that nobody actually saw Khadr throw a grenade and the leak of a document last year revealing that another militant could have done it.

It is not clear what family members in Pakistan the U.S. is concerned about. Khadr's father, a close associate of Osama bin Laden and a reputed financier of al-Qaeda operations, was killed in October 2003 by Pakistani forces.

One of Omar's older brothers, Abdullah Khadr, is in Toronto and fighting a U.S. extradition request for alleged terrorism-related crimes. His mother, sister, younger brother and grandparents are also in Toronto.

His other older brother, Adurahman, was arrested in Afghanistan as a suspected al-Qaeda member in 2001 and sent to Guantanamo Bay but was released and returned to Canada in 2003. He has claimed his father raised him to become a suicide bomber and has since distanced himself from his kin, referring to himself as the "black sheep" of the family.

Child soldiers are victims: UN official

The case against Khadr at the U.S. military tribunal in Guantanamo is adjourned until Nov. 16 while U.S. President Barack Obama decides how to proceed with Khadr and 200 other prisoners there. Obama has vowed to shut down the controversial prison at the military base in Cuba.

Coomaraswamy, the UN's top advocate for child soldiers, has been pushing for the U.S. to stop Khadr's trial and release him, arguing his age at the time of the alleged incident makes it a unique case.

"The UN position is that children should not be prosecuted for war crimes," she said.

Coomaraswamy has argued child soldiers are victims who should be rehabilitated rather than jailed. She proposed working with an organization like UNICEF Canada to create a rehabilitation program for Khadr to reintegrate him into society.

She said the UN and UNICEF Canada have been pushing both Ottawa and Washington to free Khadr, the only Western citizen still being held by the U.S. at Guantanamo Bay.

Canada's federal government is fighting a lower-court ruling upheld by the Federal Court of Appeal that required Ottawa to try to repatriate Khadr, and in August filed an appeal of the decision with the Supreme Court of Canada.

Some other Western countries have intervened to get their citizens out of Guantanamo, but the Canadian government has maintained that because of the seriousness of the charges, Khadr should face military proceedings in the United States.

The Supreme Court hearing is scheduled for Nov. 13.