Yemeni government forces waging an offensive against al Qaeda pushed into a militant stronghold in the south after militants blew up a government building there with some then withdrawing.

Yemeni government forces waging an offensive against al Qaeda pushed into a militant stronghold in the south after militants blew up a government building there with some then withdrawing, the Defense Ministry said on Tuesday.

The Defense Ministry's website quoted an official military source as saying soldiers and allied tribal militias known as popular committees had crossed into al-Mahfad.

"The source said al Qaeda elements blew up the government building in al-Mahfad," the defence ministry cited the source as saying, and some militants had fled the area afterwards.

The Yemeni army is waging a concerted offensive against insurgents in some of the most impenetrable regions of the Arabian Peninsula state.

The offensive follows a series of air strikes, including by U.S. drones that killed some 65 fighters. Last week a Yemeni official and tribal source confirmed the killing of the head of the AQAP cell in al-Mahfad.

Since 2012, al Qaeda in the Arabian Peninsula's main Yemen base has been in the mountainous al-Mahfad area of Abyan province where militants had fled after the army, with U.S. help, drove them from towns they seized during a chaotic national uprising in 2011.