Medical officials and the US blame the Saudi-led coalition, which in turn pins responsibility on the Iran-backed Houthi rebels.
At least 26 people were killed and dozens were wounded in air strikes blamed on the Saudi-led coalition near a hospital and popular fish market in the Yemeni city of Hudaida, Yemeni medical sources and aid agencies said on Thursday.
An AP report put the death toll as high as 28 after the air strikes hit close to the city's main public hospital Al Thawra. The same report also quoted rebel-run Al Masirah TV which said the attack killed 52 people and left more than 100 wounded.
Ahmed Yehia, who witnessed the attack, said body parts were scattered in the area of the strike. "There is a pond of blood outside the hospital's building," he said.
The wounded, mostly civilians, were hospitalised. The officials spoke on condition of anonymity because they were not authorised to brief the media.
At a closed session of the United Nations, US Ambassador Nikki Haley blamed today's attack on the Saudi-led coalition.
However, a coalition spokesman said the Houthi militia was behind the deaths of civilians in Hudaida, according to Al Arabiya TV.
A proxy war is playing out in Yemen between Iran and Saudi Arabia.
The United Nations Yemen mediator Martin Griffiths said on Thursday he planned to invite the warring parties to Geneva on September 6 to discuss a framework for peace talks and confidence-building measures as he tries to negotiate an end to the more than three-year conflict.
"I am very conscious that each day costs lives which might have been saved," Griffiths said.
Hudaida is the main port of the impoverished Arab country, where around 8.4 million people are believed to be on the verge of starvation, and a lifeline for millions.
The offensive on Hudaida launched in June by a coalition led by Saudi Arabia and the United Arab Emirates is the largest battle yet in a conflict that has killed more than 10,000 people.
The Saudi-led coalition backing Yemen's internationally recognised government has been seeking to retake rebel-held areas along Yemen's west coast, including Hudaida.
The coalition has been at war with the Iran-aligned rebels, known as Houthis, since March 2015.