Warplanes from a Saudi-led military coalition bombed a bus carrying workers to a factory in the southwestern Yemeni city of Taiz on Thursday, killing 10 of them, medics said.
The attack took place as battles for control of Yemen's third-largest city rage, with Gulf Arab countries backing local Islamist militias against the Iran-allied Houthi group.
A spokesman for the alliance did not respond to a request for comment.
Saudi Arabia and other Gulf Arab countries have been bombing the Houthis since late March to restore Yemen's Riyadh-based government to power and push back what they see as Iranian encroachment in their backyard.
At least 5,600 people have been killed in air raids and nationwide battles since the conflict began, and rights groups have criticized the coalition for a series of errant mass-casualty strikes, including a hospital in northern Yemen on Tuesday.
The alliance has denied responsibility for that attack and most other deadly attacks on civilian targets.