A terror tunnel passing being two schools belonging to the United Nations Relief and Works Agency (UNRWA) was discovered in the Gaza Strip on June 1 during construction work, the agency announced on its website on Friday.

The UNRWA, the UN agency in charge of Palestinian refugees, confirmed that "the tunnel has no entry or exit points on the premises nor is it connected to the schools or other buildings in any way."

Adding that it, "condemns the existence of such tunnels in the strongest possible terms."

In a 50-day campaign against Hamas, the Islamist group that controls the Gaza Strip and is considered a terrorist organization by the international community, Israel uncovered a vast tunnel network in which some 34 tunnels were destroyed.

Hamas has reportedly invested considerable resources to rebuild its network of attack tunnels over the past few years.

Spokesman for the agency, Christopher Gunness, said that the Palestinian refugee agency "has robustly intervened and protested to Hamas in Gaza."

Israel's ambassador to the UN Danny Danon sharply responded to the discovery, condemning Hamas.

"The cruelty of Hamas knows no bounds as they use the children of Gaza as human shields," he stated.

"Instead of UN schools serving as centers of learning and education, Hamas has turned them into terror bases for attacks on Israel."

Danon then called on the Secretary and General and the Security Council to intervene.

"The UN must act immediately to ensure that their structures and institutions are not being used to harbor the terror infrastructure of Hamas," he concluded.

Hamas since denied responsibility for the tunnel late Friday, saying that it "strongly condemned" the UNRWA statement and it would be exploited by Israel to "justify its crimes."

Hamas 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," the movement said, adding that it respected UNRWA's work.

This is the latest case in a series of accusations against UNRWA for its affiliations with Hamas.

Last month, a Gaza staffer was suspended by the United Nations agency after being accused of being politically active in the Islamist group.

UNRWA, he said, will seal the tunnel which was discovered during the summer holiday at a time when the schools were empty.

The UNRWA has founded schools with over 312,000 students in the West Bank and East Jerusalem, and 262,000 in the Gaza Strip.

Previous reports from various watchdog groups have suggested the curriculum in textbooks taught at Palestinian schools incited terrorism and violence against Israelis, demonizing them and promoting martyrdom.