The United Nations said Friday that a Saudi-led airstrike had killed at least 22 children and four women in Yemen as they fled a fighting zone — the second mass killing of Yemeni civilians by Saudi Arabia and its military partners in two weeks.
Mark Lowcock, the top United Nations relief official, asserted without qualification that the Saudi-led coalition warring with Yemen’s Houthi rebels was responsible for the attack, which happened on Thursday in a pro-Houthi district near the Red Sea port of Al Hudaydah. He said an additional airstrike in the area had killed four more children.
The assertion by Mr. Lowcock, in a statement on his office’s website, came as the Saudi coalition and the Houthis were accusing each other of the attack, which has underlined the vulnerability of civilians in a war that has lasted more than three years and become what the United Nations considers the world’s worst man-made humanitarian crisis.
Criticism of Saudi Arabia and its partners has been growing over thousands of civilian casualties, many of them caused by munitions fired from the coalition’s warplanes.
Humanitarian groups and antiwar activists have also aimed criticism at the United States, a main provider of the Saudi coalition’s weapons, intelligence, warplane refueling and guidance technology for missiles and bombs.
The Saudis and their partners have said they aim for military targets and go out of their way to avoid civilians. But an Aug. 9 Saudi-led aerial assault that struck a school bus in northern Yemen and killed dozens, including many children, raised new doubts about the targeting.
Congress has shown increasing concern. A defense policy bill that President Trump signed on Monday included a bipartisan provision that requires Secretary of State Mike Pompeo to certify that Saudi Arabia and a close ally, the United Arab Emirates — the two countries leading the coalition — are taking steps to prevent civilian deaths.
Mr. Lowcock, the United Nations under secretary general for humanitarian affairs and emergency relief coordinator, did not explain in the statement how he knew the Saudi-led coalition had been responsible for the latest attack, in the Al Durayhimi district about 12 miles south of Al Hudaydah.
A spokesman for Mr. Lowcock, Russell Geekie, said by phone that “U.N. partners verified the information” on the ground in Yemen.
There was no immediate response from Saudi Arabia or the United Arab Emirates.
Nikki R. Haley, the American ambassador to the United Nations, also had no immediate comment. After the Aug. 9 school bus attack, which Ms. Haley described as appalling, she exhorted the Saudis to “quickly complete their investigation into this incident, take appropriate accountability measures and release the results publicly.”
The United States has not called for an independent investigation of that attack, in contrast to the United Nations and humanitarian groups that operate in Yemen.
Human Rights Watch, an outspoken critic of the Saudi-led campaign in Yemen, said in a report released Friday that the coalition’s record of examining its own possible war crimes in Yemen has lacked credibility.
The work of the investigative body established for that purpose, known as the Joint Incidents Assessment Team, “has fallen far short of international standards regarding transparency, impartiality and independence,” Human Rights Watch said.
Mr. Lowcock said the assault on Thursday underscored what he called the need for “an impartial, independent and prompt investigation into these most recent incidents.”
In a country where three in four Yemenis need emergency assistance, Mr. Lowcock said, “parties to the conflict must respect their obligations under international humanitarian law and those with influence over them must ensure that everything possible is done to protect civilians.”
There was no way to independently ascertain the circumstances or death toll in the Thursday assault, which hit part of a group of villages where residents sympathize with the Houthis. United Arab Emirates ground forces have been trying to gain control there as they gather on the southern outskirts of Al Hudaydah.
A recent spate of fighting in the Al Hudaydah area has also hit facilities that provide health care, water and sanitation, raising alarms of a resurgence in the cholera epidemic that has ravaged Yemen twice during the war.
Mr. Geekie said United Nations officials were concerned about a possible “third wave” of the epidemic, which has infected more than one million Yemenis and killed 2,300 people since April 2017, the largest outbreak on record.
Mohammad Ali Kalfood contributed reporting.