According to the officials, dozens of people, many of them children, have been killed or injured in a Saudi-led coalition air strike in rebel-held northern Yemen.
The bus was travelling through Dahyan market in Saada province at the time.
According to the health ministry run by the rebel Houthi movement, at least 43 people lost their lives.
The Red Cross said most of the victims were under 10 years old.
The coalition, which is backing Yemen's government in a war with the Houthis, said its actions were "legitimate".
"[The air strike] conformed to international and humanitarian laws," spokesman Col Turki al-Malki said in a statement.