The Saudi-led coalition has taken part in Yemen's conflict since 2015 in support of President Abedrabbo Mansour Hadi's government in its fight against the Huthis.
But on Saturday, state news agency SPA said Riyadh's mission to the world body delivered a message to Guterres reiterating that the raid was "legitimate" and targeted Houthi leaders "responsible for recruiting and training young children".
In the wake of the USA -backed Saudi-led coalition's horrific bombing of a school bus last week that killed 40 Yemeni children and amid reports on Tuesday of dozens more civilian deaths after a new wave of Saudi bombings, Rep. Ted Lieu (D-Calif.) has sent a detailed letter (pdf) to the Department of Defense Inspector General demanding an investigation into whether Trump administration officials violated us or worldwide law by assisting the Saudis in their assault on Yemen. At least 51 people were killed in the strike and a further 79 injured. The International Committee of the Red Cross reported the same toll on Friday, citing authorities in Saada.
Mourners raised pictures of the children and shouted slogans against Saudi Arabia and its ally and key arms supplier, the United States.
The Houthi-run al-Masirah TV on Monday quoted a health official as saying another child had died from his wounds, raising the toll to 52. Saudi-led airstrikes hit passenger buses in the Dhahyan popular market in Saada on August 9, killing at least 43 people, mostly pupils under 10, and injuring 64 others.
A United States military spokeswoman said U.S. forces were not involved in Thursday's air strike.
US Defense Secretary Jim Mattis said on Sunday he has dispatched a three-star general to Riyadh to "look into what happened". The US State Department urged the alliance to "conduct a thorough and transparent investigation".
The conflict has killed almost 10,000 people since then - the vast majority of them civilians - and caused what the United Nations has described as the world's worst humanitarian crisis.
The central Yemeni city of Taiz is usually at the middle of fighting between the Saudi-backed invasion forces from the south, and the rebel Houthis in the north, with control of the nation's main highway up for grabs.
The ambassador also denounced Saudi Arabia's accusation that Iran violates UNSC Resolution 2216 on Yemen.