The Israeli army has intensified its offensive on the Gaza Strip, striking Hamas sites and killing at least 14 people on the second day of a military operation.
The offensive has set off the heaviest fighting between Israel and the Islamic militant group since an eight-day battle in November 2012.
Militants unleashed rocket salvos deep into Israeli territory and Israel mobilised thousands of forces along the Gaza border for a possible ground invasion into the Palestinian territory.
Israel's defence minister Moshe Yaalon has warned the offensive will be long-term, saying: "The operation against Hamas will expand in the coming days, and the price the organisation will pay will be very high."
Since the offensive began yesterday, Israel has attacked more than 400 sites in Gaza, killing at least 41 people.
The strikes came after militants fired more than 160 rockets at Israel, including one that reached the northern Israeli city of Hadera for the first time. The city is about 100 kilometres (60 miles) from Gaza.
The army said it attacked more than 160 sites in Gaza early today, including 118 concealed rocket-launching sites, six Hamas compounds, 10 militant command centres, weapons storage facilities and 10 tunnels used for militant activity and to ferry supplies in from Egypt.
Gaza health official Ashraf Al-Kedra said the new airstrikes killed one militant in south Gaza, an 80-year-old woman, the son, wife and neighbour of a Hamas militant, and three others whose affiliation was not known.
Israel's army said it targeted a militant with the Islamic Jihad militant group who had launched rockets toward Israel. Separately, Islamic Jihad claimed that one of its militants was killed with his mother and four siblings, but Mr Al-Kedra said they were all civilians.
Israel and Hamas are bitter enemies but until recently had been observing a truce that ended the previous hostilities in 2012.
Tensions have been rising since the kidnapping of three Israeli teenagers in the West Bank on June 12. Israel accused Hamas of being behind the abductions, although it provided no proof.
Israel launched a crackdown on the group's members in the West Bank and arrested hundreds of people. Hamas, which controls Gaza, responded by stepping up rocket fire.
The situation deteriorated last week after the bodies of the three were found, followed a day later by the abduction of Palestinian teenager in Jerusalem. He was later found burned to death in what Palestinians believe was a revenge attack. Six Jewish Israelis have been arrested.
Only four rockets were fired from Gaza towards Israel overnight, the army said, a significant decline from the large number that hit the night before, setting off air raid sirens in Jerusalem, Tel Aviv and other areas.
By early today, air raid sirens had sounded in Tel Aviv and Israel's south and the army said two rockets were apparently intercepted above the city by an anti-missile battery.
Military spokesman Lieutenant Colonel Peter Lerner said the military's aim was to take a "substantial toll" on Hamas and to deplete its rocket capabilities. He said the army would gradually ramp up its strikes on Gaza.
"The organisation is going to pay for its aggression. It is literally holding us hostage with its rockets," he said. "The country is not willing for this situation to continue."
About 2,000 people have attended a funeral for eight Palestinians, including at least one militant, four adults and two children, who were killed yesterday.
In that attack, an airstrike flattened the home of a Hamas militant in the southern Gaza town of Khan Younis. Israel's military said it had called the home shortly before the airstrike to warn civilians to leave.
A security official said the army has been telephoning homes, or firing small projectiles dubbed "knock on the roof" to warn civilians to leave buildings before demolishing homes. The official said the army also warns militants about such attacks if civilians are with them.
Palestinian president Mahmoud Abbas has called on the international community and the United Nations to "provide international protection for our people".
Speaking from the West Bank, he said in a televised statement that Hamas leaders in Gaza want to restore calm.
"I have been in contact with the regional and international parties in the last few days, particularly Hamas leaders in Gaza, and everyone I've talked to expressed his willingness to restore the truce and stop the escalation," Mr Abbas said.
He called the Israeli offensive on Gaza an "orchestrated and brutal aggression".
Israel's prime minister Benjamin Netanyahu said: "The army is ready for all possibilities. Hamas will pay a heavy price for firing toward Israeli citizens. The security of Israel's citizens comes first. The operation will expand and continue until the fire toward our towns stops and quiet returns."
The fighting stepped up as Egypt, which often serves as a mediator between Israel and the Palestinians, said it was in contact with both sides to end the violence. It was the first indication that cease-fire efforts might be under way.