UN Secretary General Ban Ki-moon will fly to the Middle East in an effort to broker and end to the violence in Gaza, an official told an emergency session of the Security Council on Friday.
Under secretary general for political affairs Jeffrey Feltman said a two-state solution was the only way to break the "seemingly endless cycle" of Israeli-Palestinian violence.
"The secretary general is prepared to do his part. He will leave for the region tomorrow to express solidarity with the Israelis and Palestinians," Feltman told emergency talks at the Council.
The UN chief will "help" Israelis and Palestinians "in coordination with regional and international actors, end the violence and find a way forward," Feltman said.
Israel warned Friday it could broaden a Gaza ground assault aimed at smashing Hamas's network of cross-border tunnels, as intensifying tank fire raised the Palestinian death toll to 285.
Two Israelis have also been killed, one soldier and one civilian.
The United Nations has demanded an immediate ceasefire between Israel, conducting air strikes and ground incursions into Gaza, and Hamas, bombarding Israeli cities with rocket attacks.
"Unless we address the root causes of the current escalation this dreadful violence will occur again and again. We cannot return to the status quo," Feltman said.
"Once calm is restored it is imperative to immediately tackle the underlying causes," he added.
Israeli ambassador Ron Prosor and his Palestinian counterpart Riyad Mansour traded accusations of blame for the latest violence.
Signup to our newsletter and follow us on Facebook and Twitter!
Prosor said the Jewish state was "forced to wage war against a terrorist group committed to our destruction."
For 10 days five million Israelis have had seconds to run to a bomb shelter as rockets have targeted the country's largest cities, he said.
"There is no country in the world that would tolerate such an assault on its citizens and Israel should not be expected to either," he said.
Prosor lashed out at international support for the Palestinian unity government, saying it provided cover for Hamas to weave incitement, violence and terror against Israelis.
Mansour, who read out the names of Palestinian dead and at one point appeared close to tears, accused Israel of inflicting "yet another disaster" on the densely-populated, narrow Gaza Strip.
If the council cannot protect Palestinians, they would "turn to the judicial bodies of the United Nations and the international system," he said, referring to the International Criminal Court.
"This savage Israeli aggression cannot be justified by any means. It is not 'self-defense' -- it is a vengeful military aggression intentionally planned and perpetrated," he said.
He said the overwhelmingly majority of casualties are Palestinian civilians, including 62 children, 24 women and 17 elderly, reading out the names of those killed in the last week.
He demanded that the council adopt a resolution condemning Israel's military operation, calling for an immediate ceasefire and the lifting of the Israeli blockade.
US ambassador Samantha Power said Hamas rocket attacks were unacceptable and that Israel had a right to defend its citizens, but called on all parties to protect civilians.
Chinese ambassador Liu Jieyi issued a stern rebuke to Israel, saying: "Whatever the excuse is, any action which causes heavy casualties among innocent civilians is unacceptable."
Beijing was ready to work to ease the Israeli-Palestinian conflict and towards peace in the Middle East, he said.