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A Muslim veteran affairs organization says it has not received reports of harassment from Islamic soldiers, contrary to claims by a relative of the man authorities say is responsible for the worst mass killing on a U.S. military base.

Abdul-Rashid Abdullah, deputy director of the American Muslim Armed Forces and Veterans Affairs Council, told FoxNews.com that the nonprofit group has not received a single report recently of a U.S. soldier being harassed "simply because he was Muslim."

"That kind of report is inconsistent with what we've heard," Abdullah said prior to a press conference in Washington to denounce Thursday's shooting at Fort Hood, Texas, that left 13 dead and 38 wounded. Maj. Nidal Malik Hasan, a 39-year-old Army psychiatrist who was reportedly due to be deployed later this month, is accused in the mass shooting.

Abdullah said his organization, which condemned the "unspeakable" attack, serves "several thousand" Muslim soldiers.

SLIDESHOW: Deadly rampage at Fort Hood Army Base

Hasan was shot four times during the Thursday attack and remained unconscious early Friday. He reportedly had told relatives in Virginia that he began having second thoughts about his military career after fellow soldiers harassed him for being a Muslim.

Hasan's aunt, Noel Hasan, of Falls Church, Va., told The Washington Post her nephew wanted out of the military following the Sept. 11, 2001, terror attacks due to harassment about being a Muslim.

"Some people can take it and some people cannot," she told the newspaper. "He had listened to all of that and he wanted out of the military."

Nawar Shora, legal director of the American-Arab Anti-Discrimination Committee, expressed his sympathies to the victims and their relatives on Friday.

"We were all shocked at the tragedy yesterday at Fort Hood and the act of cowardice by the attacker," Shora said. "We were all attacked yesterday. Let's remember that this was an attack on all Americans and it’s a time for all Americans to come together in unity and in faith."

Alejandro Beutel, government liaison for the Muslim Public Affairs Council, said the Muslim-American community is "appalled" by the incident.

"We unequivocally denounce this heinous act against our brave men and women serving in the military to protect our country," Beutel said. "We pray for [the victims'] well-being and for the safety of the entire nation."

Lt. Col. Les Melnyck, a Defense Department spokesman, said that as of August, 3,557 active duty troops of roughly 1.4 million identified themselves as being Muslim. According to the self-reported figures, the largest religious preference identified was Roman Catholic (284,000), followed by "no preference," he said.

"It's self-reported so you don't have to fill in that box," Melnyck said, adding that 1,710 Muslims are currently serving in the Army, by far the most of any service branch.