Al-Qaeda-affiliated Ansar al-Sharia claimed its fighters took over the 19th Infantry Brigade in Bihan in the southeast of Yemen.
In a Twitter post on Thursday, the group said it controlled a military camp in Bihan.
A local source confirmed the takeover, but Yemeni officials haven't been able to verify the claim.
Yemen has been in limbo since its president and prime minister resigned less than two weeks ago after the Shiite Houthi militias seized the presidential palace and confined the head of state to his residence in a struggle to tighten control over Yemen.