The United States and the United Nations condemned an attack on a UN school in the Gaza Strip that was sheltering displaced Palestinians.

Gaza officials said Israel shelled the school, killing 15 and wounding 90.

The IDF said it fired back at the school after soldiers were targeted by mortar rounds launched from the area.

White House spokeswoman Bernadette Meehan said the US was “extremely concerned” that thousands of Palestinians aren’t safe in UN-designated shelters in Gaza.

Meehan added that the US also condemns those responsible for hiding weapons in UN facilities in Gaza and said the escalation shows the need for an immediate ceasefire.

Earlier Wednesday, UN Secretary General Ban Ki-moon condemned the strike on the school. Ban asserted that the shelling was “unjustifiable” and called for those responsible to be held to account.

“This morning a UN school sheltering thousands of Palestinian families suffered a reprehensible attack,” Ban said during a visit to Costa Rica.

Heavy smoke billows following an Israeli military strike in Gaza City on July 29, 2014 (Photo credit: Ashraf Amra/AFP)

Heavy smoke billows following an Israeli military strike in Gaza City on July 29, 2014 (Photo credit: Ashraf Amra/AFP)

“It is unjustifiable, and demands accountability and justice.”

Ban accused the IDF of ignoring repeated communications on the location of the school.

“I want to make it clear that the exact location of this elementary school has been communicated to the Israeli military authorities 17 times, as recently as last night, just a few hours before this attack,” he says.

“They are aware of the coordinates and exact location of where these people are.”

France also condemned the shelling of the UN school, calling for an immediate ceasefire.

President Francois Hollande “joins the UN secretary general (Ban Ki-moon) in considering the act ‘unjustifiable,’” the president’s office said in a statement.

Paris “demands the establishment of an immediate ceasefire,” the statement said, adding that “all efforts must converge on this goal.”

Israel’s security cabinet instructed the IDF Wednesday to continue to “forcefully hit Hamas and the other terrorist organizations in Gaza,” and to conclude its mission to destroy the tunnels leading from the strip into Israel, a diplomatic source said.

So far, the army’s actions in locating and destroying terror tunnels have brought about significant strategic achievements in an area in which Hamas has invested much effort over the years, the source said.

“The IDF also has significant achievements in damaging the terrorist infrastructure of Hamas and additional terrorist groups and will continue act and expand these operations,” the source added.

Palestinian sources said that at least 76 people were killed Wednesday in Israeli strikes across Gaza, raising the Palestinian death toll above 1,300 since the IDF first started operating in the Strip. Israel asserts that hundreds of those killed throughout the operation were Hamas or Islamic Jihad fighters.