At least 82 people have been killed and more than 500 injured in a strike on a funeral gathering in the Yemeni capital, Sanaa, rebel officials say.
The Houthi-run government said the hall had been hit by an air strike carried out by the Saudi-led coalition backing the internationally-recognised government of Yemen.
The coalition has denied carrying out a strike, suggesting "other causes".
Thousands of civilians have been killed since the war began in 2014.
The attack targeted the funeral of the father of Houthi-appointed Interior Minister Galal al-Rawishan, an ally of the rebels and of former President Ali Abdullah Saleh.
One rescuer, Murad Tawfiq, described the scene as a "lake of blood", the Associated Press news agency reports.
Graphic photos circulating on social media show charred and mutilated bodies.
The International Committee of the Red Cross (ICRC) said it had prepared 300 body bags.
The ICRC's Rima Kamal told the BBC "several air strikes" had hit the venue where hundreds of civilians had been present.
The damage to the buildings was extensive.
A number of Houthi rebel military and security officials are believed to have been killed in the strike.
BBC correspondents say their presence could explain why the funeral was targeted, though it is likely many civilians were also there.
The government of President Abdrabbuh Mansour Hadi is fighting both the Houthis and forces loyal to Mr Saleh.
Image copyright Reuters Image caption Saudi Arabia joined the war on the side of President Hadi in March 2015
Thousand of civilians have been killed since the Saudi-led air campaign started last March, the UN's rights body says.
Nearly three million people have been displaced in Yemen, one of the region's poorest countries, since the war began in 2014.
The Houthis took the capital then, forcing Mr Hadi's government to flee. Some ministers have since returned to the city of Aden.
