Apache helicopters fired rockets at the village of Bani Zela in Hajjah province, 10 km (6.5 miles) from the Saudi border, on Sunday, killing at least 25 civilians, including women and children, the residents and medics said.
The helicopters returned for a second strike as residents and medical teams were trying to evacuate casualties, killing three medics and two more civilians, they said, Reuters reported.
"People were fleeing their homes as the helicopters pursued," a resident who identified himself as Khaled, told Reuters by telephone. "They committed a massacre for no reason."
Yemen's Saba news agency, run by the Houthi group now in control of much of the country and under attack by a Saudi-led coalition of Arab states, put the death toll at 28 and said 17 others were injured, some seriously.
"Rescue teams and medics are still working on transfering the casualties to safety," the agency said, quoting an official in the province.
A Saudi official claimed the coalition had played no role in any attack in the area.
"This is totally false news. We deny it," the official, who declined to be identified, told Reuters, adding that no coalition helicopters operated so far from the border.
The coalition has been pounding the Houthi group from the air for six months, trying to eject it from the capital Sana'a and restore fugitive former president Abd-Rabbu Mansour Hadi to power.
The campaign has resulted in several mass killings of civilians, including 36 people at a water bottling plant in August and 25 workers at a milk factory in April.
The target of Sunday's strikes was unclear, but the border area has recently been the scene of clashes between Yemen's Houthis and Saudi forces.
Sunday's attack came less than a day after Saudi Arabia announced that a brigadier general died in hospital of wounds suffered in an incident on the border with Yemen.