The Defense Ministry said the deadliest attack in Sayoun took place near a military barracks, where a suicide car bomb destroyed large parts of an adjacent date-processing plant, killing at least nine civilians, including two children and a woman.
A security official said that a number of people are believed to have been buried under the rubble and rescue teams are working to retrieve the bodies. The ministry said the bomber was targeting the barracks but was stopped by security forces outside the compound.
An airplane carrying passengers from the capital Sanaa, which was making a transit stop in Sayoun en route to Dubai, was caught in the crossfire, officials said.
The military deployed tanks and heavy weapons, and eventually forced the militants out, security officials said.
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While the airport and the military barracks were under attack, militants in pick-up trucks shelled the main post office in the city, setting parts of the building on fire, but were forced to retreat by security guards, the ministry said.
The attacks appeared to be in retaliation for an earlier raid by security forces in the city, where seven suspected al-Qaida militants were arrested, including a local leader.
The Yemeni government launched a major offensive in the spring in an attempt to drive al-Qaida militants from their southern strongholds. The United States is financing most of the government operations and providing logistical support in addition to launching drone strikes against the insurgents.