Saudi-led coalition warplanes killed 36 soldiers on Wednesday when they targeted a rebel troop headquarters in the Yemeni capital as the United Nations tried to reschedule postponed peace talks.
The coalition campaign of air strikes against Iran-backed Shiite Huthi rebels and allied forces loyal to former leader Ali Abdullah Saleh began on March 26 in an effort to restore UN-backed President Abedrabbo Mansour Hadi to power.
On Wednesday, warplanes launched a raid on the command headquarters of special forces loyal to Saleh in southern Sanaa, as well as on an arms depot in the Fajj Attan neighbourhood overlooking the city, residents said.
An official from the rebel-held health ministry told AFP that "36 soldiers and officers were killed and 100 others were wounded" in the raids, raising an earlier toll of 15 dead.
Other air raids on Wednesday badly damaged a rebel-controlled naval base in the province of Hodeida on the Red Sea coast, residents said.
Strikes also hit the northern rebel stronghold province of Hajja near the border with Saudi Arabia, witnesses said, reporting casualties in seven raids on arms depots at Abs military base.
In the southern province of Daleh, the coalition launched an early morning attack on a rebel-held military camp north of the provincial capital.
Anti-rebel militiamen have been trying to retake the camp, and clashes there have killed more than 60 fighters on both sides over the past 48 hours, a local government official said.
Pro-Hadi forces said on Tuesday they had regained control of the provincial capital itself, also named Daleh.
The coalition also raided other rebel positions in the central city of Dhammar and in Taez province, as well as in oil-rich Marib in the east, residents said.
The United Nations is trying to reschedule peace talks for Yemen that had originally been due to begin in Geneva on Thursday.
It says almost 2,000 people have been killed and more than half a million displaced in the conflict since the fighting escalated in March with the air campaign.
World Health Organization chief Margaret Chan said on Wednesday that the toll includes "hundreds of women and children", adding that "almost 7.5 million people are in urgent need of medical help".
"Hospitals around the country are closing down their emergency operations rooms and intensive care units due to shortages in staff and fuel for generators," Chan said.
"The health and lives of millions of people are at risk."
She urged all parties to "respect their obligations under international humanitarian law to protect civilians, health facilities and health staff during conflict and to permit the supply of vital humanitarian aid".
Relief agency Oxfam warned on Tuesday that at least 16 million Yemenis, or two thirds of the population, had no access to clean drinking water because of the conflict.
UN Secretary General Ban Ki-moon has instructed his special envoy to step up efforts with all factions in Yemen and countries in the region to agree on a ceasefire and a new date for talks, his spokesman said on Tuesday.
This week's Geneva talks were scrapped after Hadi demanded that the rebels withdraw from territory they have seized before the negotiations begin.
The United Nations had called for the talks to be held without preconditions.