Al-Qaeda in the Arabian Peninsula jihadists established strongholds in towns and rugged zones in Abyan and Shabwa provinces after security forces chased them from major cities in Abyan in 2012.
Yemeni and US drone strikes last week targeted bases of AQAP, considered by Washington as the most dangerous affiliate of the global jihadist network with links to several failed terror plots against the United States.
Army troops backed by local militiamen had moved in to "purge" the Abyan towns of Ahwar and Al-Mahfad, and Azzan, Al-Houta, Al-Rawda and Al-Saeed in Shabwa province, a military official told AFP.
Government forces clashed today with Islamist militants in the Lahmar area, which overlooks Al-Mahfad, a military commander said.
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Other confrontations took place near Al-Saeed as militants took on advancing government forces, other military sources said.
Hussein al-Wuhayshi, a leader of the Popular Committees armed groups that had fought in the past alongside government forces, said his forces were taking part in the attack.
"There is an official decision to uproot Al-Qaeda from Abyan and Shabwa," Wuhayshi told AFP.