At least three people are reported dead and nine wounded after clashes broke out on Tuesday in the Yemeni capital Sanaa between the army and around 200 members of the elite Republican Guard.
Heavy gunfire was reported around the Defence Ministry and extra soldiers were sent to defend the building.
Military sources told Reuters that three had been killed and nine wounded.
The Republican Guard is under the command of the son of the former president Ali Abdullah Saleh who stood down in February after many months of protests.
It is thought the Guards are unhappy at a military shake-up announced by the new president Abdrabbuh Mansour Hadi.
Under the plan some units would fall under the control of a new Presidential Protection Force, while others would be subject to different regional commands.
Observers said the move was intended to dilute some of the power of the Republican Guard, and that their reaction was a direct challenge to government authority.