Local media say Saudi-led warplanes have hit a building where hundreds of people had gathered for a funeral. Reports suggest several Houthi military officials are among the casualties.
According to the United Nations, the airstrikes by the Saudi-led coalition on mourners in Sanaa killed dozens of people.
"Initial reports from health officials in Sanaa indicate that over 140 people were killed and over 525 injured," said the statement from the UN humanitarian coordinator in Yemen, Jamie McGoldrick.
The Shiite Houthi-controlled "sabanews.net" said the strike targeted a hall where a condolence-offering ceremony was being held.
It published pictures showing several charred or mutilated bodies, adding that a hospital was still receiving those badly injured from the latest deadly violence in a two-year old civil war.
The bombardment destroyed the hall and triggered a big fire, the news site cited a rebel security source as saying.
Rebels said people had gathered at the building to pay their respects to the father of the rebel interior minister Jalal al-Rowaishan, adding that the minister's fate was unknown.
The casualties include Houthi military and security officials who are fighting the internationally recognized government of President Abed Rabbo Mansour Hadi.
Yemeni military leader killed
Also on Saturday, Yemen's army announced the death of its most senior commander to be killed this year.
Major-General Abdul-Rab al-Shadadi was killed while leading an offensive against the Houthis east of the capital on Friday.
Three militia commanders fighting alongside the army of the internationally recognized government were also killed.
Backed by Iran, Houthi rebels had swept into Sanaa in September 2014 and advanced across much of the country, forcing the internationally recognized government of Abed Rabbo Mansour Hadi to flee the capital.
More than two-thousand people were killed between July 2015 and June 2016, according to UN figures; close to half of them died in airstrikes carried out by a coalition led by Saudi Arabia.
The Saudi-led alliance has come under intense scrutiny in recent months over the allegedly high civilian death toll from its aerial campaign.
dm/rc,lw (AFP, AP, dpa)