Armed tribesmen attacked an army post in southeast Yemen on Sunday and killed four soldiers in the latest assault targeting security forces in the area since December, a military official said.

The attack took place near Shahr in Hadramawt province, which has been hit by protests against the central government since last month, after the army killed tribal chief Said Ben Habrish and his bodyguards at a checkpoint.

Gunmen and troops traded fire after the attack, witnesses said, adding that army reinforcements had arrived in the area.

The military official said a regional tribal alliance was behind the attack.

In addition to attacks on the army, the recently formed alliance of tribes in Hadramawt has sabotaged pipelines in the region at least two times in recent weeks.

On Saturday, members of the alliance killed two soldiers and wounded another in an attack on oil installations operated by Norwegian DNO in Hadaramawt, a security official had said.

Hadramawt was part of the formerly independent South Yemen, which was unified with the north in 1990.

A secession attempt four years later sparked a brief but bloody civil war that ended with northern forces taking over the south.

Southern grievances have hindered the political transition following the 33-year rule of Ali Abdullah Saleh, who stepped down last year following Arab Spring-inspired protests.