"Gunmen on a motorbike opened fire at air force Colonel Mahmoud al-Naqib, killing him instantly," an official in the southern province of Lahij told AFP, adding that the assailants fled.
The attack was carried out by militants "suspected of belonging to Al-Qaeda," the official added.
Farther east on the border between the provinces of Marib and Shabwa, troops of the 119th Infantry Brigade which was attacked on Thursday by Al-Qaeda handed over their remaining arms to local tribes and withdrew from the area, local officials said.
Another official said the jihadists took "30 tanks, 90 military vehicles, 25 armoured vehicles and 28 artillery pieces".
The militants later handed over the camp to tribes but kept the heavy weapons, officials said.
Al-Qaeda in the Arabian Peninsula (AQAP), considered by Washington as the jihadist network's most dangerous branch, has accused the troops of links with the Shiite militiamen ruling Sanaa.
AQAP frequently attacks both Yemeni security forces and Western targets.
UN Secretary General Ban Ki-moon warned on Thursday that Yemen was "collapsing before our eyes" as several countries shut their embassies in Sanaa and evacuated their staff.
Yemen's Sunni-dominated neighbour Saudi Arabia was the latest to evacuate staff from its Sanaa mission on Friday, citing a "deteriorating security and political situation".
