Israel has accused Hamas, Islamic Jihad and other militants of using the protests, women, children and the elderly as a cover to infiltrate into Israel to commit terrorist attacks, he said.

As those protests continue, tension and the potential for serious incidents and further casualties will increase, he warned.

"Israel must calibrate its use of force and minimize the use of live fire. Lethal force should be used only as a last resort. Hamas and the leaders of the demonstrations must keep protestors away from the Gaza fence and to prevent all violent actions and provocations."

Children, who should be particularly protected, are at grave risk, said Mladenov, noting that at least four children have been shot dead by Israeli live fire.

"I take this opportunity to reiterate, in the strongest possible terms, that civilians, particularly children, must not be intentionally put in danger or targeted in any way."

In other incidents, two Hamas militants were shot dead on March 30 in an exchange of fire near Gaza's fence and five rockets and mortars were fired toward Israel in the last month.

On April 12, one person was killed by an Israeli airstrike after a group of Palestinian militants targeted an Israeli aircraft with machinegun fire. At least three additional militants were killed by Israeli security forces in separate incidents, said Mladenov.

On April 15, the Israeli security forces announced it had sealed the fifth Hamas tunnel in the past six months leading from Gaza into Israel.

The Israeli security forces also foiled an attempt in the West Bank to smuggle 10 pipe bombs that were reportedly intended for an attack on Israel's independence day, he said.

All militant activity in Gaza, including the digging of tunnels and the firing of rockets, must cease, he said. "It threatens the lives of Israelis and Palestinians alike, increases the risk of a new escalation of hostilities, undermines calls for lifting the closures, and ultimately damages the prospects for peace."

What is happening in Gaza is an injustice that no man, woman or child should have to endure: the deplorable living conditions; the consequences of the continued, suffocating closures and control by Hamas; and the mounting risk that Gaza could trigger a new conflict, he said.

Palestine remains a central part of the regional quagmire. Until the occupation ends and a two-state solution is achieved through meaningful negotiations based on relevant UN resolutions, the conflict will remain one of the key drivers of extremism and a persistent threat to regional stability, he warned.