Ten children were killed and 28 other children were wounded on Saturday when an airstrike struck a school in northern Yemen, medical humanitarian organization Doctors Without Borders said.

All the casualties were 8-15 years old, the group, which uses its French acronym, MSF, posted on Twitter.

Yemeni officials say that the U.S.-backed, Saudi-led coalition was responsible for the attack, the Associated Press reports.

As Reuters explains, "Saudi Arabia and its allies have launched thousands of air strikes against the Houthis since they drove the internationally recognized government into exile in March 2015."

The Saudi-led coalition, however, denied targeting a school. Agence France-Presse reports that coalition spokesman Gen. Ahmad Assiri said that the site bombed was "a major training camp for militia," adding that the death toll as recorded by MSF "confirms the Al Houthi practice of recruiting and subjecting children to terror."

"When jets target training camps, they cannot distinguish between ages," he said, according to the news agency.

Assiri also said, according to the New York Times, "They [Houthi rebels] use civilian installations as the command and control centers of their organization." He added, "Don't focus on the technical details. This is a war. Collateral damage could happen, mistakes could happen."

UNICEF issued a statement Saturday in response to the attack, saying, in part: "With the intensification in violence across the country in the past week, the number of children killed and injured by airstrikes, street fighting, and landmines has grown sharply."

The Washington Post, which also reports that Yemeni and local officials described it as a coalition strike, writes that the force "dramatically stepped up its air assault Tuesday after five months of relative calm."

The New York Times' reporting also notes two addition coalition strike on Saturday, one of which also killed children.

One bombardment in the village of Birken in the Razih District, near Yemen’s northern border with Saudi Arabia, struck the home of Ali Okri, a school principal, killing his wife and four of their children. Then, in what has become known in the war here as a double tap, a second airstrike killed four more of Mr. Okri’s relatives as rescuers were trying to free them from the rubble.

The new strikes come a day after the United Nations expressed concern over the increase in violence in the war-torn country. Jamie McGoldrick, the UN Humanitarian Coordinator in Yemen, stated, "A political solution is the only solution to this crisis."

"The people of Yemen continue to bear the brunt of the suffering as a result of the inability of the parties to find a political solution to a conflict that has been raging for more than a year and a half. The return to full-scale hostilities only drives humanitarian needs further," he added. According to the Norwegian Refugee Council, 6,500 people have been killed, roughly half of whom are civilians, in the last 500 days, and nearly 20 million have no access to clean water.

And earlier this month, Julien Harneis, UNICEF representative in Yemen, said, "Children are paying the heaviest price of the conflict in Yemen."

The agency's Mohammed al-Asaadi also warned this month that at least 370,000 children in the country were at risk of starvation.

As Common Dreams reported last week, "Saudi Arabia and its military coalition have been the target of criticism from both the United Nations and Human Rights Watch for alleged breaches of international humanitarian law that many say amount to war crimes."

Amid all this, "a lot of nations would be looking to distance themselves from the disastrous failure," Jason Ditz wrote at Antiwar.com. "Not the U.S., however, as they brag up their escalating support for the Saudi air war."