At least 30 Yemeni pro-government fighters were killed in a Saudi-led coalition air strike that "mistakenly" hit one of their positions in southern Yemen on Saturday, medics and witnesses said.
Another 40 people were wounded in the strike on Waziya, an area between Taez and Lahj provinces where rival forces have been fighting since late September, the sources said.
The Arab coalition is backing loyalist troops against Iran-backed rebels in Yemen with air strikes, weapons and ground forces.
Pro-government forces retook Lahj as part of a southern offensive in mid-July that recaptured four other provinces.
But fighting has raged for months in the southwestern province of Taez, seen as a gateway to the capital, held by the rebels since last year.
Local residents told AFP that the rebels have sent reinforcements to Waziya in a bid to re-enter Lahj and once more control the strategic Al-Anad airbase.
Around 4,500 civilians have been killed in the conflict since March.