United Nations officials discovered a tunnel built under a school in the Gaza Strip run by UNRWA, the international body’s agency for Palestinian refugees, the global body said in a statement.

Since the discovery some two weeks ago, UNRWA closed the school and sealed off the opening to the tunnel. The school resumed operations last Wednesday, the UN organization said.

The statement Saturday did not say where the tunnel led, where it was found, or who was believed to have constructed it.

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“The presence of a tunnel underneath an UNRWA installation, which enjoys inviolability under international law, is unacceptable. It places children and agency staff at risk,” the agency said.

UNRWA informed Israel’s Coordinator of the Government Activities in the Territories, IDF Maj. Gen. Yoav Mordechai, of the incident and also lodged a complaint with the relevant authorities in Gaza over the violation of the neutrality of a UN facility, according to a Sunday report from the Hebrew-language Ynet website.

Over the years, Gaza’s Hamas terrorist rulers have built a labyrinth of tunnels, some passing under the border into Israel which they used to launch attacks during their last conflict with the Jewish state in 2014.

On June 1, UNRWA said it found “part of a tunnel that passes under two adjacent agency schools in the Maghazi camp” during construction work.

At the time, Israel’s Ambassador to the United Nations Danny Danon submitted a letter of protest to UN Secretary-General Antonio Guterres and the UN Security Council.

Hamas later “strongly condemned” the UNRWA revelation, saying it would be exploited by Israel to “justify its crimes.”

The terror group denied it built the tunnel and said it had clarified the issue “with all factions and resistance forces, who clearly stated they had no actions related to the resistance in the said location.”

UNRWA has long been criticized by Israel for aspects of its handling of relations with Hamas, and Israel has claimed that some of UNRWA’s Palestinian employees support terrorist activities and spread anti-Semitism online.

An independent UN inquiry found in 2015 that Palestinian armed groups hid weapons in three empty UN-run schools in Gaza and that in at least two cases terrorists “probably” fired rockets at Israel from the facilities during the summer war in 2014 between Israel and the Gaza Strip.