Col Terry Lee, a retired officer who worked with him at the military base in Texas, alleged Maj Hasan had angry confrontations with other officers over his views.
Maj Hasan was reportedly fighting orders to be deployed to Iraq at the end of the month, claiming that he was the victim of harassment and insults because of his Arab background and his faith.
The major is a psychiatrist who had been treating soldiers returning from Iraq for post-traumatic stress and alcohol and drug abuse problems.
“He was making outlandish comments condemning our foreign policy and claimed Muslims had the right to rise up and attack Americans,” Col Lee told Fox News.
“He said Muslims should stand up and fight the aggressor and that we should not be in the war in the first place.” He said that Maj Hasan said he was “happy” when a US soldier was killed in an attack on a military recruitment centre in Arkansas in June. An American convert to Islam was accused of the shootings.
Col Lee alleged that other officers had told him that Maj Hasan had said “maybe people should strap bombs on themselves and go to Time Square” in New York.
He claimed he was aware that the major had been subject to “name calling” during heated arguments with other officers.
Federal law enforcement officials have said Maj Hasan had come to their attention at least six months ago because of internet postings that discussed suicide bombings and other threats.
The officials said the postings appeared to have been made by Maj Hasan but they were still trying to confirm that he was the author.
Maj Hasan’s cousin Nader Husan said he was happy working for the military but did dread deployment to Iraq.
Mr Hasan said his cousin was a US-born Muslim who had joined the military after high school. He had served as a psychiatrist at the Walter Reed Army Medical Center in Washington DC, which treats many badly wounded troops.