UNITED NATIONSinfo-icon - The United Nations said Friday that a Saudi-led airstrike had killed at least 22 children and four women in Yemeninfo-icon as they fled a fighting zone -- the second mass killing of Yemeni civilians by Saudi Arabiainfo-icon and its military partners in two weeks.

Mark Lowcock, the top United Nations relief official, asserted that the Saudi-led coalition was responsible for the attack, which happened on Thursday in a district near the Red Sea port of Al Hudaydah. He said an additional airstrike in the area had killed four more children.

The latest attack underlined the vulnerability of civilians in a warinfo-icon that has lasted more than three years and become what the United Nations considers the worldinfo-icon'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 the USinfo-icon supplies munitions fired from the coalition's warplanes.

This is the second time in two weeks that an airstrike by the Saudi-led coalition has resulted in dozens of civilian casualties.

A Saudi air attack on a bus in the northern rebel stronghold of Saada on Aug. 9 killed 40 children, prompting U.N. Secretary-General Antonio Guterres to call for an independent investigation.

Lowcock renewed the U.N. appeal for "an impartial, independent and prompt investigation" and said "those with influence" over the warring sides must ensure that civilians are protected.

Saba news agency said the airstrike on Thursday hit a bus and a house.

Al-Durayhimi lies 12 miles (20 kilometers) south of Hodeida and has seen two weeks of fighting between the rebels and pro-government forces backed by the UAEinfo-icon.

"I had hoped that the outrage that followed the Saada attack in Yemen two weeks ago would be a turning point in the conflictinfo-icon. Yesterday's reported attacks in Al-Durayhimi, killing 26 children, indicate that it was not," said Henrietta Fore, the director of the U.N. children's agency, UNICEF.

Fore urged the warring sides, their foreign backers and the Security Council to "take action and end this conflict once and for all."

After widespread condemnation of the August 9 bus attack, the coalition announced that it was opening an investigation, but rights groups insist any probe should be impartial.

In a 90-page report, Human Rightsinfo-icon Watch said the coalition had failed to properly investigate war crimes allegations stemming from attacks on civilian targets.

HRW's Middle Eastinfo-icon director, Sarah Leah Whitson, said the coalition's investigators "were doing little more than covering up war crimes."

The European Unioninfo-icon urged Yemen's warring sides to "prioritize the protection of civilians in all instances" following the attacks in Al-Durayhimi and stressed the need to end the war, according a statement from the EU foreign affairs spokesperson.

U.N.-brokered talks between Yemen's government and the Ansarullah led rebel movement are to open in Geneva on Sept. 6 -- a first step toward resuming peace negotiations that broke down two years ago.

The Security Council has called for a "credible" investigation of the bus attack in Yemen but did not demand an independent probe.

Three of the five permanent council members -- Britaininfo-icon, Franceinfo-icon and the United Statesinfo-icon -- are supporting the Saudi coalition in its military campaign. Non permanent member Kuwaitinfo-icon is part of the coalition.

Yemen's Ansarullah movement, which plays a significant role in aiding the Yemeni armyinfo-icon in defending the impoverished country against the invading coalition, condemned the Thursday attack, saying the blood of children was spilled again before that of those killed in the bus attack dried. 

Saudi Arabia and some of its allies, including the United Arab Emiratesinfo-icon, Morocco and Sudaninfo-icon, launched a brutal war, code-named Operation Decisive Storm, against Yemen in March 2015 in an attempt to reinstall Abd Rabbuh Mansur Hadi, Yemen's fugitive president and a staunch ally of Riyadh back to power. 

The imposed war initially consisted of a bombing campaign, but was later coupled with a naval blockade and the deployment of ground forces to Yemen.

The war has left tens of thousands dead and unleashed what the United Nations describes as the world's worst humanitarian crisis.