Israel has said it will not bow to international pressure to end air strikes in Gaza that officials there said had killed almost 100 Palestinians, despite an offer by US President Barack Obama to help negotiate a ceasefire with militants.
Asked if Israel might move from the mostly aerial attacks of the past four days into a ground war in Gaza to stop militant rocket fire, Prime Minister Benjamin Netanyahu replied: "we are weighing all possibilities and preparing for all possibilities".
"No international pressure will prevent us from acting with all power," he told reporters in Tel Aviv a day after a telephone conversation with Obama about the worst flare-up in Israeli-Palestinian violence in almost two years.
Washington also affirmed Israel's right to defend itself in a statement from the Pentagon.
But Defence Secretary Chuck Hagel told Israeli Defence Minister Moshe Ya'alon he was concerned "about the risk of further escalation and emphasised the need for all sides to do everything they can to protect civilian lives and restore calm".
A rocket caused the first serious Israeli casualty — one of eight people hurt when a fuel tanker was hit at a service station in Ashdod, 30km north of Gaza, and Palestinian militants warned international airlines they would fire rockets at Tel Aviv's main airport.
Medical officials in Gaza said at least 75 civilians, including 23 children, were among at least 99 people killed in the aerial bombardments which Israel began on Tuesday. They included 12 killed today.
Palestinian President Mahmoud Abbas urged the United Nations Security Council to order an immediate truce.
But Israel said it was determined to end cross-border rocket attacks that intensified last month after its forces arrested hundreds of activists from the Islamist Hamas movement in the occupied West Bank following the abduction there of three Jewish teenagers who were later found killed.
A Palestinian youth was killed in Jerusalem in a suspected Israeli revenge attack.
Israel's campaign "will continue until we are certain that quiet returns to Israeli citizens", Netanyahu said. Israel had attacked more than 1,000 targets in Gaza and there were "more to go".
Israel's military commander, Lieutenant-General Benny Gantz, said his forces were ready to act as needed - an indication of a readiness to send in tanks and other ground troops, as Israel last did for two weeks in early 2009.
"We are in the midst of an assault and we are prepared to expand it as much as is required, to wherever is required, with whatever force will be required and for as long as will be required," Mr Gantz said.
Western-backed Abbas, who is based in the West Bank and agreed a power-sharing deal with Gaza's dominant Hamas in April after years of feuding, called for international help:
"The Palestinian leadership urges the Security Council to quickly issue a clear condemnation of this Israeli aggression and impose a commitment of a mutual ceasefire immediately," he said.
The rocket salvoes by the hardline movement and its allies, some striking more than 100 km (60 miles) from Gaza, have killed no one so far.
Israeli leaders have hinted they could order troops into the Gaza Strip, a 40-km sliver of coastline that is home to nearly two million people.
Some 20,000 reservists have already been mobilised, the army says.
UN doubts over strikes
The United Nations human rights chief has voiced serious doubts that Israeli's military operation against Gaza complied with international law banning the targeting of civilians.
International law requires Israel to take all measures to ensure that its attacks are proportional, distinguish between military and civilian objects, and avoid civilian casualties, UN High Commissioner for Human Rights Navi Pillay said.
Ms Pillay said: "We have received deeply disturbing reports that many of the civilian casualties, including of children, occurred as a result of strikes on homes.”
“Such reports raise serious doubt about whether the Israeli strikes have been in accordance with international humanitarian law and international human rights law," the statement added.