Thousands of people have gathered in Yemen for the funerals of dozens of children killed in a Saudi-led coalition attack on a bus last week.

The mass burial took place in Saada, a northern stronghold of Houthi rebels.

Crowds chanted in protest at Saudi Arabia, which backs the Yemeni government's fight against the group.

The coalition initially said its actions were "legitimate", but later said it would probe "collateral damage".

The children's bodies were wrapped in white shrouds and carried in cars bearing the Houthi logo.

Local authorities say 51 people - including 40 children - were killed in the air strike on a bus travelling in Dahyan, in Saada province, last Thursday.

Most of the children were aged between 10 and 13.

On Monday, the foreign affairs minister of the United Arab Emirates - which is part of the coalition - appeared to justify the use of force in the air strikes.

"War is not something that can actually be a clean operation," said Anwar Gargash, according to the Associated Press news agency.

Houthi officials have labelled the raid a "crime by America and its allies against the children of Yemen".

The coalition against the rebels receives logistical and intelligence support from the US, UK and France.

The UN Secretary-General Antonio Guterres has called for an "independent and prompt investigation" into the air strike.