The Yemeni army has sent reinforcements to the port city of Mukalla to retake an army headquarters overrun by gunmen.
At least three soldiers and two attackers were killed when 30 gunmen in army uniforms attacked the compound.
Some soldiers managed to escape but others are still inside the headquarters, which is surrounded by armoured vehicles.
Yemen is struggling to control general lawlessness, an al-Qaeda insurgency, and divisions within the army.
Officials say the militants drove up to the army headquarters in stolen military trucks, firing at security guards and setting off explosives at the main gate.
They took control of the compound, in the south-eastern province of Hadramawt, and are reported to have taken a number of hostages.
Yemeni army reinforcements have been deployed to the headquarters, and have cordoned off the surrounding area.
On 20 September, suspected al-Qaeda fighters killed at least 40 soldiers and police in simultaneous attacks on military targets in the neighbouring province of Shabwa.