The attack on a military base in Abyan, which two of the sources said killed at least two soldiers and injured over 20, comes as the recognized government and a separatist group both mass fighters in the area while Riyadh moves to ease tensions.
The Southern Transitional Council (STC) has been vying with the Saudi-backed government for control of the south. The Houthis, who ousted the government from the Yemeni capital, Sanaa, in late 2014, largely hold the north.
There was no immediate comment from the Houthis, who are trying to seize the government's last northern stronghold in gas-rich Marib while also keeping up cross-border attacks on Saudi cities.