For the second time this month the United Nations has blamed the Saudi-led forces fighting in Yemen's civil war for an airstrike that killed children.There were conflicting reports about the death toll in the strike, which occurred Thursday, and about who committed it. But the United Nations top humanitarian officialissued a statement blaming the attack on the Saudi-led forces, saying that at least 26 people were killed including 22 children and four women."This is the second time in two weeks that an airstrike by the Saudi-led Coalition has resulted in dozens of civilian casualties," said Mark Lowcock, U.N. undersecretary general for humanitarian affairs.On Aug. 9, U.N. Secretary General Antonio Guterres blamed the Saudi-led coalition for an airstrike that hit a school bus killing at least 50 people.The two statements — both unusually strong for the U.N. — highlight the growing concern over what appear to be especially indiscriminate attacks in a war already marked by high civilian casualties.The coalition said the school bus strike was targeting Houthi militants that had fired a missile. There had not been a response reported as of Friday afternoon to the reports of the attack Thursday.Members of the U.S. Congress and human rights advocates have objected to U.S. support for the Saudi-led coalition, which includes targeting information, weapons sales and mid-air refueling of planes. CNN reported that the bomb that hit the school bus was U.S.-made.The civil war started with a 2014 uprising by a faction led by the Houthis —a Muslim religious minority. In 2015, the Houthis captured the capital ousting the sitting, Saudi-backed government. That was when the Saudi's formed a coalition with the United Arab Emirates and other allies to join the battle against the Houthis with air forces and ground troops.Yemen, a rugged, poor country, has had a history of localized battles. But this war has escalated and intensified with the Saudi-led coalition's entry. The coalition says it's fighting the Houthis because they're backed by Iran and note that the Houthis have fired missiles into Saudi Arabia.The U.N. said earlier this month that it had documented 6,592 civilians killed since the coalition entered the war in 2015 — saying coalition attacks account for most of them. The war has also led to food shortages and the spread of disease.There were conflicting reports about Thursday's strike. The Associated Press reported Houthisources saying an attack in the ad-Durayhimi district near the port city of Hodeidah killed 30 people. The AP said that there were also accounts saying just nine were killed.The state news service for the UAE — a member of the Saudi-led coalition — reported that the Houthis fired a missile at a village in the area that killed one child and injured dozens of other people. It was unclear if this referred to the same incident the Houthis blamed on the coalition.The statement by the U.N.'s Lowcock, blaming the coalition, came out after those reports.Also Friday, Human Rights Watch released a reportsaying the Saudi-led coalition has failed to credibly investigate allegations of war crimes in Yemen. The report looked at 75 reported investigations by a team of investigators the coalition said would collect evidence and delve into cases of civilian casualties.Human Rights Watch said the investigations failed to meet international standards of independence and transparency and did not hold officers responsible for their actions.The report said the countries supporting the coalition need to press for better accountability. "Those countries that continue to sell weapons to Saudi Arabia — including the U.S., U.K. and France — risk complicity in future unlawful attacks, particularly given that coalition assurances to take action have proven hollow," it stated. Copyright 2018 NPR. To see more, visit http://www.npr.org/.