Yemeni soldiers ride on an armoured personnel vehicle during fighting against Houthis in the frontline province of Marib, in this Sept. 24, 2015 photo.

Loyalist forces in Yemen backed by a Saudi-led coalition killed at least 20 Iran-backed insurgents Saturday, the military said, as they pressed their offensive on the rebel-held capital Sanaa.

Twelve other rebels were captured in the operation launched on the northwestern edge of Maarib province, a key battleground in the fight for control of the capital, said a military official

“Loyalist forces, supported by coalition aircraft, have made a slight advance” in the northwest of Maarib, Abda Al-Subei, of the provincial security forces, told AFP.

Subei said Saturday’s operation came a day after coalition airstrikes on rebel positions.

He did not elaborate on the overall progress of the offensive.

But another Yemeni officer, Murad Turiq, said ground forces came across land mines planted by rebels and were also having difficulty moving through the mountainous region.