The rocket, which landed in Ashkelon, reportedly caused some damage but no injuries. It marks the first breach of the Egyptian-brokered ceasefire agreement of 21 November, which brought an end to eight days of violence in Gaza and Israel.

Robert Serry, the UN Special Coordinator for the Middle East Peace Process, said he was “deeply troubled” by resumed indiscriminate rocket fire from Gaza, which is “totally unacceptable.”

Today’s developments, according to a statement issued by Mr. Serry’s office, only underscore the importance of ongoing Egyptian efforts to solidify the truce brokered last November.

In his briefing to the Security Council, Under-Secretary-General for Political Affairs Jeffrey Feltman also underscored the “troubling” nature of today’s incident and stressed the need to inject new life in the political process aimed at reaching a two-State solution.

“We know that there are negative forces on both sides, such as those who fired today’s rocket from Gaza into Israel, who draw strength from stalemate and paralysis,” he stated, adding that both sides have a responsibility to marginalize these forces by creating the conditions, including trust, for a successful negotiating process.

“As demonstrated today in the troubling rocket attack fired from Gaza into Israel, the temperature is again rising between Israelis and Palestinians – with the situation of Palestinian prisoners the most immediate but not only cause – and there is yet no process of negotiation to offer hope on the horizon.”

The UN continues to follow the issue of Palestinian prisoners in Israeli custody, and had voiced concern at the news of the death on Saturday in Israeli detention of Arafat Jaradat. Yesterday, Mr. Serry called for an independent and transparent investigation into the circumstances of Mr. Jaradat’s death, which occurred just a few days after his arrest.

Mr. Feltman described as “a most troubling development” that, earlier today, Gaza militants from the Al-Aqsa Martyrs Brigade cited this death in claiming responsibility for the rocket attack. The prisoner’s death has also sparked a series of demonstrations and clashes, which have reportedly resulted in the injuries of 43 Palestinians by Israeli security forces.

It is a moment of “heightened risks across multiple fronts” in the Middle East, the Under-Secretary-General pointed out, noting that Syria continues to be a source of “extreme concern” for the world body.

The nearly-two-year-old conflict has left over 4 million people in need of humanitarian assistance, including 2 million internally displaced, and led more than 900,000 people to flee to neighbouring countries, including over 150,000 this month alone, he stated.

“Even tentative steps to dialogue are struggling to take root,” Mr. Feltman added. “The destructive military spiral churns more forcefully each day and threatens to pull its neighbours, most notably and worrisomely Lebanon, into its vortex.

“Opportunities do exist to reverse these trends, but not if the international community sits still. Stepped up efforts by this Council and its members can make a substantial difference while there is still time to do so.”

Israel launched over 100 attacks on sites across the Gaza Strip on Tuesday, bombing the headquarters of a bank and the home of a Hamas commander, according to Maan news agency.

The Israeli military has struck more than 1,350 targets in Gaza since attacks began on Wednesday, in an operation to deter Palestinian fighters from launching rockets into its territory.

Since then, 640 rockets have hit Israel while more than 300 others have been intercepted by Israel’s anti-missile system, the Iron Dome, according to the Israeli army. Three Israeli civilians died on Thursday in a rocket strike.

The Israeli military said that 67 rockets had been fired at the country on Monday, and that three Israelis had been wounded while more than 30 people were killed in Gaza on Monday, according to Al Jazeera.

Meanwhile, the UN agency assisting Palestinian refugees expressed its concern for the rising death toll reiterating its call for all sides to stop the violence.

“The situation [for civilians] is bad,” said the spokesperson for the UN Relief and Works Agency for Palestinian Refugees in the Near East (UNRWA), Christopher Gunness. “This is a very densely populated place. There are many, many civilians. More than half of Gaza’s 1.7 million people are children, and what we are seeing are rockets flying out of this area, populated largely by civilians, and airstrikes coming in.”

“We are echoing the call of Secretary-General Ban Ki-moon in appealing to all sides to exercise utmost restraint, to de-escalate so that peace can begin to take hold,” Mr. Gunness said. “All sides must honour their obligations under international humanitarian law to protect civilians.”

Efforts are also underway in Cairo for reaching a truce. Egypt has been trying to broker a ceasefire with the help of Qatar and Turkey.

Khaled Meshaal,  the Hamas leader, said on Monday his group was committed to efforts to secure a truce, but insisted that Israel must lift its six-year blockade of the Gaza Strip.

During a briefing to reporters this afternoon, Mr. Ban’s spokesperson said Mr. Ban will meet with Egyptian President Mohamed Mursi and the Secretary-General of the League of Arab States, Nabil El-Araby today, and, later this week, with Israeli Prime Minister Benjamin Netanyahu and the President of the Palestinian Authority, Mahmoud Abbas.

On Tuesday the Turkish Foreign Minister Ahmet Davutoglu and various Arab foreign ministers are also expected to visit Gaza on Tuesday.