The coalition said the strike targeted the Iran-backed Huthi rebels responsible for a deadly missile attack on the Saudi city of Jizan on Wednesday.
"Targeting Saudis and residents in Saudi is a red line", coalition spokesman Turki al-Malki later told Al Arabiya TV.
The head of the humanitarian organisation's delegation in the country, Johannes Bruwer, later tweeted that "scores" had been killed and "even more injured, most under the age of 10".
A spokesman for the Red Cross in Sanaa told AFP the toll was not final as casualties from the attack had been taken to several different hospitals.
State Department spokeswoman Heather Nauert said the U.S. was "concerned" by reports of an attack resulting in civilian deaths. "The Secretary-General emphasizes that all parties must take constant care to spare civilians and civilian objects in the conduct of military operations". He asserted that it evinces a "blatant disregard for rules of war when [a] bus carrying innocent school children is fair game for attack".
"Save the Children condemns this horrific attack and is calling for a full, immediate and independent investigation into this and other recent attacks on civilians and civilian infrastructure", it said.
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An airstrike in the north reportedly killed at least 50, more than half of them children.
Qassemi further said the countries involved in acts of aggression against Yemeni people resort to such statements in an attempt to cover up their criminal acts and divert world public opinion from the realities on the ground in the war-ravaged country.
A doctor treats children injured by the airstrike.
Video footage, which CBS News can't independently verify, appear to show the devastating aftermath.
The Houthis seized the capital, Sanaa, in 2014 and overthrew the internationally recognised government led by President Abdrabu Mansur Hadi during a transition of power from former president Ali Abdullah Saleh.
A Saudi Arabian blockade has contributed to starvation and disease while a United Nations report found the Saudi-led bombing campaign - carried out with USA support - has hit schools, even weddings.
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He criticized Riyadh for denying Iranian delegates entry visas for OIC summits, saying such statements "are compiled and released unilaterally and unjustly under pressure from Saudi Arabia". "The attack today was a follow-up process to neutralise that threat".
The missile was sacked from the rebel-held Yemeni province of Amran towards Jizan, the coalition said.
Saudi Arabia intercepted a ballistic missile fired by Yemen's Houthi rebels on Wednesday, but shrapnel killed a Yemeni man and wounded 11 others in the southern Saudi city of Jazan, the Arab Coalition said.
They say their missile attacks on the kingdom are in retaliation for air raids on Yemen by the Western-backed coalition.
Global aid agencies denounced the attack and the loss of civilian lives. Just one week ago, an air raid in Hodeidah seaport claimed the lives of 55 civilians.
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