A further 14 soldiers were wounded when the bomber drove an explosives-laden car into an army position in Abyan province, said the official.
The same source previously said the attack had killed six and wounded 18.
Jihadist groups including al Qaeda in the Arabian Peninsula (AQAP) and the Islamic State group have carried out numerous attacks in the region.
Yemen cross-border shelling kills Saudi child
Yemen's army is simultaneously fighting Huthi rebels who control the northern capital Sanaa and extremist groups in the south.
A Saudi-led Arab military coalition that backs the Yemeni government of President Abedrabbo Mansour Hadi has also turned its sights on AQAP, targeting it with air strikes.
The United States has carried out numerous drone strikes against AQAP operatives in Yemen.
AQAP and IS have escalated their attacks in recent months, notably in the southern port city of Aden.
That is despite efforts by government forces to stabilise urban areas they have controlled since ousting Huthi forces from Aden last year.
A suicide car bombing targeting young army recruits in Aden killed some 71 people on August 29. It was claimed by IS.
The Saudi-led coalition launched its military campaign in March 2015 as Huthi rebels closed in on Hadi in his refuge in Aden, forcing him into exile.
Backed by the air power and ground support of the coalition, government forces pushed the rebels out of five southern provinces last summer.
The conflict in Yemen has left 6,600 people dead since the Saudi-led intervention, according to the United Nations.
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