Palestinian militants indicated they were ready for a truce with Israel on Monday to defuse a growing crisis after four days of rocket strikes from the Gaza Strip into the south of the Jewish state.
There was no immediate response from Israel which has warned it is ready to ramp up its air strikes and shelling if the rockets do not cease.
Leaders of Hamas, the Islamist faction that controls Gaza, met with Islamic Jihad and other groups on Monday night and said they would respond according to the way Israel acted - a formulation used in previous flare-ups to offer a ceasefire.
"If (Israel) is interested in calm they should stop the aggression," Sami Abu Zuhri of Hamas told Reuters.
The Palestinian people were acting in self-defense, he said.
"The ball is in Israel's court. The resistance factions will observe Israel's behavior on the ground and will act accordingly," said Khaled Al-Batsh of the Islamic Jihad group.
Throughout the day, Israel warned it was ready for stronger action. Prime Minister Benjamin Netanyahu convened foreign ambassadors in what an apparent move to pre-empt international censure should Israel, whose 2008-2009 Gaza offensive exacted a high civilian toll, again go in hard.
Netanyahu briefed the envoys in Ashkelon, a port city within range of some Palestinian rockets. "None of their governments would accept a situation like this," he said.
He was due to convene his close forum of nine senior ministers on Tuesday to decide a course of action. Israel Radio said Defence Minister Ehud Barak and military chief Lieutenant-General Benny Gantz had met with Netanyahu on Monday night to present possible attack scenarios.
Environment Minister Gilad Erdan, an influential member of Netanyahu's Likud party, said the briefing was meant to prepare world opinion for "what is about to happen", adding there might be a major Israeli escalation within a few hours.
"Hamas bears responsibility. The heads of Hamas should pay the price and not sleep at night. I expect to see not just a return to targeted killings, but also to very wide activity by (the army)," he told Israel Radio.
Hamas took part in some missile launches at the weekend but it did not claim responsibility for attacks earlier on Monday, suggesting it was looking to step back from the brink.
The Israeli military said Palestinians had fired 12 rockets on Monday, and a total of 119 had been launched since Saturday.
Netanyahu said a million Israelis - around one-eighth of the population - were in danger. Israel has been deploying its Iron Dome rocket interceptor, air raid sirens and blast shelters, but eight people have been wounded by the rockets.
Six Palestinians, including four civilians, have been killed by Israeli shells fired on Gaza since Saturday, and at least 40 have been wounded.
EGYPT IN THE PICTURE
A Palestinian official who declined to be named said Egypt had been trying to broker a ceasefire and although no formal truce was in place, Hamas understood the need for calm.
Monday's launches were claimed by smaller groups, including a radical Salafi organization that rejects Hamas's authority.
Israel has shown little appetite for a new Gaza war, which could strain relations with the new Islamist-rooted government in neighboring Egypt. The countries made peace in 1979.
But Netanyahu may be reluctant to seem weak ahead of a January 22 election that opinion polls currently predict he will win.
Israel said the latest flare-up started on Thursday with a fierce border clash. On Saturday, a Palestinian missile strike wounded four Israeli troops patrolling the boundary, triggering army shelling of Gaza in which the four civilians died.
In turn, dozens of mortars and rockets were launched at Israel, which carried out a series of air strikes in Gaza.
Additional reporting by Ari Rabinovitch and Maayan Lubell in Jerusalem, Editing by Ori Lewis, Douglas Hamilton and Andrew Heavens