A Saudi-led coalition air strike on rebels in a residential area of the Yemeni capital on Tuesday killed at least 21 people including civilians, witnesses and medics said.
The raid targeted Iran-backed Houthi insurgents in the Sabeen neighbourhood of the rebel-held capital Sanaa, but nearby homes were also damaged, witnesses said.
"At least 21 Houthis and residents were killed in the raid," a medical source told AFP, without being able to specify the number of civilian fatalities.
The death toll is likely to rise because some people are missing, another medical source said, as rescuers combed the rubble.
The Arab coalition launched an air war against the Shiite rebels in March, when the advancing insurgents forced President Abedrabbo Mansour Hadi to flee to neighbouring Saudi Arabia.
The United Nations says nearly 4,900 people have been killed in the conflict. The UN aid chief has called the scale of human suffering "almost incomprehensible".
On Monday the rebels celebrated the first anniversary of their seizure of Sanaa, which they overran unopposed, aided by renegade troops loyal to ousted president Ali Abdullah Saleh.