Airstrikes from the Saudi-led coalition targeting Yemen’s Shiite Houthi rebels mistakenly struck a pro-government military encampment, killing at least 20 fighters and wounding another 20 in the latest instance of friendly fire in the anti-rebel camp, security officials said Saturday.

The fighters had just wrestled the encampment from the Houthis in the southern Taiz province when airstrikes hit them, pro-government security officials said.

“They thought the Houthis were still there,” one pro-government security official told The Associated Press.

Ground commanders have repeatedly complained of slow communication with military leadership in Riyadh, the officials added.

Yemen’s fighting pits the Houthis and allied army units against forces loyal to the coalition-backed internationally recognized government as well as southern separatists and other militants.

Also Saturday, Saudi airstrikes killed 13 Houthis in the massive desert province of Jawf, neutral security officials there said. The strikes are part of a plan to seize the northern province in order to advance on the Houthi heartland of Sadaa, pro-government officials said.

A day earlier, gunmen on a motorcycle killed an Emirati officer in the southern port city of Aden, the sixth assassination of pro-government troop leaders and officials there in recent weeks, pro-government security officials said.

The United Arab Emirates is part of the Saudi-led coalition, which has been pounding rebel positions since March.

Although no group has claimed responsibility for the attack, pro-government officials said they suspect Sunni extremists, who they say have made land grabs, exploiting the chaos engulfing the Arab world’s poorest country. Yemen’s al-Qaida, viewed by Washington as the terror network’s most dangerous affiliate, is known to have used motorcycles in previous assassinations.

Also Saturday, al-Qaida militants set up security checkpoints and began enforcing sex segregation at the sole college in Zinjibar, the provincial capital of Abyan, neutral and pro-government security officials there said.

“First they took Mukalla and then Zinjibar. We are all worried Aden may be next,” one pro-government security official told The Associated Press.

Yemen’s al-Qaida branch overran Mukalla, the capital of sprawling Hadramawt province, in April. They have since gender-segregated public spaces there and publicly killed and flogged people, including on charges of “witchcraft,” Mukalla residents told The Associated Press last week.

All officials and witnesses spoke on condition of anonymity because they are not authorized to brief reporters or fear reprisals.