The Saudi-led coalition, under mounting criticism over the civilian death toll of its bombing campaign against the rebels since March, denied any involvement in the latest attack.
It was the second alleged coalition air strike on a Yemeni wedding party in just over a week.
The new raid hit a house where dozens of people were celebrating the wedding on Wednesday evening in the town of Sanban, 100 kilometres (60 miles) south of the capital Sanaa, residents said.
"Coalition warplanes launched the attack. The house was completely destroyed," said witness and local resident Taha al-Zuba.
"Warplanes were heard in the area ahead of the attack."
The rebels' Almasirah television said on Twitter that the wedding was hit by "aggression warplanes", referring to the coalition.
Medical sources said another 38 people were wounded.
Coalition spokesman Brigadier General Ahmed al-Assiri said the allies did not launch any air strikes in Dhamar.
"We did not conduct any operation in Dhamar... No strikes there, definitely," he told AFP.
In September a suspected coalition strike killed at least 131 civilians at a wedding near the Red Sea city of Mokha, which the UN said may have been the deadliest single attack since March.
The coalition again denied involvement.
The latest strike came as the United Nations announced that the rebels, who control the capital and much of central and northern Yemen, had accepted a UN Security Council resolution calling for an end to the seven-month conflict.
The rebels' refusal to agree to abide by Resolution 2216 passed in April -- demanding their withdrawal from all the territory they have seized since they overran the capital in September 2013 -- had stymied previous peace efforts.
President Abedrabbo Mansour Hadi, who fled into exile in neighbouring Saudi Arabia in March but whose forces have since recaptured much of the south with the support of Saudi-led ground troops, had refused to join UN-brokered peace talks until the rebels signed up.
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But UN spokesman Stephane Dujarric announced in New York late on Wednesday that both the rebels and their allies had confirmed they were willing to enter talks based on the UN resolution.
"This is an important step," he said.
The Shiite Huthi rebels, whose heartland is in the mountains of the far north, were able to capture much of the country because of the support of renegade troops still loyal to Hadi's ousted predecessor Ali Abdullah Saleh.
Saleh's party, the General People's Congress, also announced on Wednesday that it had accepted the UN peace plan following secret talks with UN envoy Ismail Ould Cheikh Ahmed.
But a member of Hadi's delegation, Abdulwahab al-Homayqani, said the rebels "did not announce their commitment to implement UN Resolution 2216" demanding their withdrawal.
- Rights group criticism -
Human rights watchdogs have repeatedly criticised the Saudi-led Arab coalition's air strikes in Yemen, saying they have hit areas without any military targets.
In late August, an air strike hit a bottled water factory in the northern province of Hajja, killing 17 civilians and 14 rebels.
Warplanes in July struck staff residences at a power plant in the Red Sea port of Mokha, killing 65 civilians, while an April raid on a dairy plant in the port of Hodeida further north left 35 civilians dead.
The rebels too have come under heavy criticism from rights groups for "indiscriminate" shelling of civilian-populated areas.
A Western-backed resolution calling for a UN investigation into abuses committed during the Yemen conflict was withdrawn due to protests from Saudi Arabia, Human Rights Watch said last week.
"It's truly a missed opportunity," said Philippe Dam of HRW. "What explains it? It was Saudi Arabia's total opposition" to the Dutch text.
The United Nations says around 5,000 people have been killed in the conflict in impoverished Yemen over the past seven months, many of them civilians.