Seven people, including four kids, were killed when an airstrike hit a Save the Children-backed hospital in Yemen, the international organization said Tuesday. Eight others were injured in the assault and two adults are missing.

"The hospital had been open for only half an hour and many patients and staff were arriving on a busy morning," Save the Children said in a news release. "They included a health worker who died along with their two children."

A missile hit mid-Tuesday morning close to the entrance of the hospital, located in Yemen's northwest, the organization said. "The missile was said to have landed less than 50 yards from the facility's main building," it added.

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The organization's CEO and president, Carolyn Miles, said the hospital is one of many "delivering life-saving aid to children living in what is the worst place on earth to be a child."

"These children have the right to be safe in their hospitals, schools and homes. But time after time, we see a complete disregard by all warring parties in Yemen for the basic rules of war," Miles said. "Children must be protected. We must stop this war on children."

Earlier this month, the executive director of the United Nations Children's Fund (UNICEF), said eight children are killed or hurt every day in Yemen, across 31 "active conflict zones."

"Talks and conferences have so far done little to change the reality for children on the ground," the executive director, Henrietta Fore, said. "Only a comprehensive peace agreement can give Yemeni children the reprieve from violence and war that they need and deserve."