Six Yemeni soldiers were killed in a tribal revenge attack on Saturday in the southeastern province of Al-Baida, a tribal leader and a security official said. \"Gunmen attacked an army checkpoint near Radaa, killing six soldiers,\" the tribal leader said, describing it as a \"revenge killing.\" The root of the enmity was not immediately clear but a security official confirmed the attack. Such incidents are common in Yemen, an impoverished deeply tribal country on the Arabian Peninsula. Yemen has been gripped by deadly protests since late January calling for the ouster of President Ali Abdullah Saleh who has been in power since 1978. The protests have led to defections and clashes within the army. In addition to anti-regime protests, Yemen has been battling a secessionist movement in the south, a Shiite rebellion in the north and an Al-Qaeda resurgence on its soil.