The UN envoy for the Middle East warned on Tuesday of catastrophic consequences from escalating violence in Gaza as the Palestinian group Hamas and Israel continued to exchange fire despite a truce.
Nickolay Mladenov told the Security Council that a "fragile calm" had returned to the region but that the situation remained "extremely tense", after reports that Hamas had agreed to a truce.
"I am concerned that we may once again be facing another very dangerous escalation of violence in Gaza, with potentially catastrophic consequences," Mr Mladenov told a council meeting on the Middle East.
"The last two days have shown how close we came to the brink of war once again."
The UN is working with Egypt to ensure the truce takes hold to avoid the outbreak of a fourth war in the Palestinian enclave.
The Israeli military said that it launched 15 attacks across Gaza, in the second day of cross-border fighting with Hamas.
The increase in violence follows an attack by Hamas on Monday, when a rocket fired from Gaza hit an Israeli house, wounding seven people.
Retaliatory Israeli air strikes in Gaza destroyed targets that included the office of Hamas leader Ismail Haniyeh.
The group said extra Israeli soldiers and tanks had been moved to the border.
Israeli Prime Minister Benjamin Netanyahu, who cut short a visit to the US to deal with the crisis, said Israel might take further action in Gaza.
"We are prepared to do a lot more," Mr Netanyahu said in a satellite TV address from the American Israel Public Affairs Committee in Washington.
"We will do what is necessary to defend our people and to defend our state."
He is in a tight race for re-election against former army chief Benny Gantz.
The Israeli army said nearly all of the rockets fired on Monday and Tuesday were intercepted by the Iron Dome missile defence system or landed in open areas.
Mr Haniyeh warned Israel against heavy retaliation. He said the Palestinian people "will not surrender" and its militant factions "will deter the enemy if it exceeds the red lines".
At least two Israeli missiles destroyed a commercial building in central Gaza City, wounding two, the official Palestinian news agency reported.
A third Palestinian was injured in a strike east of Ash Shajaya, inside Gaza City. Gaza's Health Ministry said seven Palestinians have been wounded.
In Israel, air raid sirens sounded, schools and roads closed and bomb shelters opened.
Across the border, Hamas leaders went into hiding, police and security installations were evacuated and hospitals were on alert. But the vast majority of Gazans do not have access to bomb shelters.
"A new conflict will be devastating for the Palestinian people," Mr Mladenov said.
"It will have consequences for Israelis, who live in the vicinity of the Gaza perimeter and it is likely to have regional repercussions."
He also said that Israel's settlement expansion in the West Bank and East Jerusalem had continued despite a 2016 resolution demanding an end to building the Jewish outposts.
More than 3,000 units have been approved or tendered in the occupied West Bank, which is the largest batch of new settlements since May 2018, Mr Mladenov said.
Mr Netanyahu came under heavy criticism from allies and opponents for what they say is ineffective policy against Gaza militants.
He has held indirect ceasefire talks through Egyptian mediators in recent months, and even allowed the delivery of millions of dollars of aid to Hamas to ease harsh conditions in Gaza.
"The reality in which Hamas turned Israel into a hostage is unprecedented and unfathomable," his chief challenger, Mr Gantz, wrote on Twitter on Monday.
He led the army during the last Gaza war in 2014.
Mr Netanyahu also came under attack from his own nationalistic allies.
"Israel's deterrence has collapsed and it has to be said in all honesty that Netanyahu has failed against Hamas," said Education Minister Naftali Bennett, head of the Yamin HeHadash faction in the prime minister's coalition.
Meanwhile in Lebanon, Hezbollah Secretary General Hassan Nasrallah met a delegation from Hamas led by Saleh Al Arouri.
