The army intelligence chief, Brigadier Gen. Osvaldo Montero, was fired for "professional reasons, according to the government news agency, which gave no further reason for the departure.
The Defense Ministry confirmed Montero's departure but also did not elaborate.
The Argentine daily Clarin reported that Montero was sacked because he had tried to prevent Garre's recent reappointment as defense minister.
Garre has been defense minister under President Nestor Kirchner and President-elect Cristina Fernandez recently announced that Garre will remain in the post after she takes office Dec. 10.
As defense minister, Garre has revamped military education, placed a greater emphasis on human rights and undertaken other reforms. A former leftist activist, Garre reportedly also has had run-ins with officers opposed to her changes.
In May 2006, she sacked five army officers who wore uniforms while attending an event in support of the 1976-1983 military dictatorship, a period during which thousands of suspected dissidents were arrested and killed.