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's army is simultaneously fighting Huthi rebels who control the northern capital Sanaa and jihadist groups in the south.
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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.
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.