A coalition of Saudi Arabia and the United Arab Emirates said on Saturday that the aerial attack on a school bus in Yemen last month was “unjustified” and expressed its regret, reported Reuters. An air raid on August 9 at a market in Saada province killed 51 people, including 40 children in a bus.

The alliance, backed by the United States, is battling with Houthi rebels aligned with Iran. The Joint Incident Assessment Team said that the air raids were carried out after intelligence inputs indicated the presence of Houthi leaders in the bus.

“There was a clear delay in preparing the fighter jet at the appropriate time and place, thus losing [the opportunity] to target this bus as a military target in an open area in order to avoid such collateral damage,” said legal advisor of the Joint Incident Assessment Team, Mansour Ahmed al-Mansour. The Joint Incident Assessment Team is an investigative body set up by the coalition.

“The team believes that the coalition forces should immediately review the application of their rules of engagement to ensure compliance,” al-Mansour said. Later, the coalition accepted the JIAT findings and said it would take legal action against those who contributed to the mistake. “The Joint Forces Command of the Coalition expresses regret over the mistakes, extends its sympathies, condolences and solidarity to the families of the victims,” it said in a statement.

The Joint Forces Command will revise its rules of engagement to ensure that such incidents do not happen again, it added. It will also coordinate with the Yemen government to compensate victims.

Pentagon spokesperson Dana White said that the US Department of Defense welcomed the announcement of the findings, saying the country appreciated the coalition’s decision to take legal measures to ensure accountability and make the necessary improvements to prevent another tragedy.

But Hussain al-Bukhaiti, a pro-Houthi activist, said the statement was “not an apology” and “added insult to injury”. “Since the beginning of this war, they have committed many crimes and they only regret or release such a statement only if that crime has been covered widely on the media,” Al Jazeera quoted him as saying.

Human Rights Watch on Sunday called the attack “an apparent war crime” and called on all countries to immediately halt weapons sales to Saudi Arabia. It also sought an independent inquiry by the United Nations into the violations.

“The Saudi-led coalition’s attack on a bus full of young boys adds to its already gruesome track record of killing civilians at weddings, funerals, hospitals, and schools in Yemen,” said Bill Van Esveld, senior children’s rights researcher at Human Rights Watch. “Countries with knowledge of this record that are supplying more bombs to the Saudis will be complicit in future deadly attacks on civilians.”