Brazilian President Luiz Inacio Lula da Silva fired the army commander, General Julio Cesar de Arruda, on Saturday, a source with knowledge of the matter said.
The firing of Arruda, who had been commander since Dec 28, was reported earlier on Saturday by Brazilian newspaper Folha de S Paulo and TV network Globonews. His replacement will be General Tomas Miguel Ribeiro Paiva, army commander of the southeast, the source said.
Brazil's army and the Ministry of Defense did not immediately comment on the matter.
Lula said this week that intelligence services failed on Jan 8, when government buildings in Brasilia were stormed by supporters of far-right former president Jair Bolsonaro.
Previously, Lula said he suspected collusion by "people in the armed forces" in the insurrection, during which several thousand Bolsonaro supporters invaded and ransacked the Congress building, the presidential palace and the Supreme Court.
Arruda had attended a meeting with Lula on Friday, accompanied by the commanders of the navy, Marcos Sampaio Olsen, and air force, Marcelo Kanitz Damasceno.
Defense Minister José Múcio Monteiro told reporters after the meeting that the Jan 8 riots were not the main discussion topic, but added that any involvement of military personnel in the riots would be punished.
Lula has said recently that his government would purge hardcore Bolsonaro loyalists from the security forces. Many of the demonstrators who rioted in Brasilia called for a military coup to restore Bolsonaro to power.