Palestinian students look inside a classroom that witnesses said was shelled by Israel during its offensive, on the first day of the new school year east of Gaza City, Sept 14, 2014. [Photo/Agencies]

JERUSALEM - The UN Middle East envoy said on Tuesday that Israel and the Palestinians had reached a deal over the reconstruction of the Gaza Strip, following Israel's recent seven-week offensive known as Protective Edge.

"The UN Special Coordinator for the Middle East has brokered a trilateral agreement between Israel, the Palestinian Authority and the United Nations to enable work on the scale required in the Gaza Strip," UN Special Coordinator for the Middle East Peace Process Robert Serry told the UN Security Council in New York on Tuesday.

Serry briefed the Security Council over the developments in the region following the Aug 26 ceasefire that put an end to fifty days of fighting between Israel and Hamas-led Gaza militants. He said the Palestinian Authority would lead the rehabilitation efforts in the strip.

"A lead role (would be given) to the Palestinian Authority in the reconstruction effort, while providing security assurances through UN monitoring that these materials will not be diverted from their entirely civilian purposes," Serry said.

The envoy referred to the entry of materials needed to reconstruct the strip through the passages, assuring Israel that they would not be used for military purposes as they have in the past, like the construction of underground smuggling tunnels.

He described the state of devastation in the strip as "shocking," specifically addressing the damage caused to infrastructure, hospitals and schools amid Israeli air strikes and shelling. More than 2,100 Palestinians were killed in the fighting, mostly civilians, while on the Israeli side, 66 soldiers and six citizens lost their lives.

The Palestinian Authority estimated that the cost for rehabilitating the strip would amount to $7.8 billion, two and half times more than the gross domestic product in the strip, the Ha'aretz daily reported.

Regarding the Egypt-brokered ceasefire agreement that ended the fighting on Aug 26, Serry said the calm is sustained but is "worryingly fragile," adding that some underlying topics still need to be addressed by both parties. "Gaza could implode, or explode again," he warned.

According to various reports, Israel and the Palestinians are set to resume negotiations later this month in order to come to terms over key issues for reaching a permanent truce. But there are no indications of these talks taking place anytime soon.

Despite the ceasefire, a rocket or mortar shell fired from the Gaza Strip landed in Israeli territory on Tuesday evening, causing no injury or damage, the Israeli army confirmed. It was the first projectile fired from Gaza since the ceasefire was agreed upon three weeks ago.