Israel's intense bombardment of the Gaza Strip has killed at least 27 people and wounded 130 others, Palestinian officials have said.
Israel on Tuesday said it was ready for a long-term offensive against Hamas in the Palestinian territory after a surge in rocket attacks on Israeli towns.
"We are preparing for a battle against Hamas which will not end within a few days," Defence Minister Moshe Yaalon said in a statement.
Israeli said it had undertaken more than 273 airstrikes against the strip on Tuesday.
The Israeli cabinet has authorised the calling up of 40,000 army reservists ahead of a possible ground offensive. At least 1,500 soldiers have already been deployed around the perimeter of Gaza.
Hafez Hamad, one of the leaders of the al-Quds Brigades, the military wing of Islamic Jihad, was killed in a strike on his home in Beit Hannoun, neighbours and hospital officials said.
Two children, two females, and one adult male were also reported killed in the attack.
At least five children were among 12 others killed in Gaza on Tuesday, Palestinian officials said.
Palestinian President Mahmoud Abbas appeared on Palestinian TV late on Tuesday to appeal for international help as renewed conflict between Israel and Hamas continued to escalate.
Abbas said he had been in touch with the various Palestinian factions and leaders of Hamas who, he said, did not want an escalation.
"What's happening in the Gaza Strip, the West Bank, and East Jerusalem is not a war between two armies," he said.
"The Palestinian people are an unarmed people, people who live under occupation.
"It's time now for the international community, and especially the Quartet and the Security Council to take their responsibility to guarantee the international protection of our people."
'Iron Dome' deployed
The renewed violence came a day after nine Palestinians were killed after more than 60 Israeli airstrikes struck the Gaza strip on Monday. Palestinian fighters launched more than 80 rockets that day.
Following the worst outbreak of violence along the Gaza frontier since an eight-day war in 2012, the Israeli military said a ground invasion was possible, though not imminent, and urged citizens within a range of 40km of the coastal territory to stay close to bomb shelters.
Israelis ran for cover as sirens sounded in Tel Aviv in the deepest attack from Gaza since hostilities flared three weeks ago after the abduction and killing of three young Israeli settlers.
Some rockets were apparently intercepted by Israel's "Iron Dome" missile defence system.
Air raid sirens later sounded in Jerusalem, where dozens of rockets landed close to the city. Israel said other areas targeted included Beer Sheva, Ashdod and Ashkelon
The Israeli military said that in the past 24 hours, more than 100 rockets had been fired at its territory.
Some were intercepted by the Iron Dome anti-missile system, but two people were wounded by shrapnel.
The Israeli military said that more than 200 rockets have been launched at Israel from the Gaza Strip since Israel mounted the dragnet while searching for the missing settlers.
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Of those killed on Tuesday, seven died in an air strike in the town of Khan Yunis, south of Gaza. At least 25 were injured in that attack.
Palestinian medical officials said that at least four were killed in a drone strike that hit a vehicle in al-Wahda Street in the centre of Gaza.
Earlier on Tuesday, an air raid targeted a site belonging to the al-Qassam Brigades, the military wing of Hamas, killing one person.
US backs Israel
Explosions echoed across the Gaza Strip on Tuesday, shaking buildings and sending smoke rising from targets hit by Israeli fire.
In residential areas, the sounds of crying children could be heard as ambulance sirens wailed. Some people took to rooftops to watch for Israeli aircraft and rockets streaking towards Israel.
"We will not tolerate rocket fire against our cities and townships, and therefore I ordered a significant broadening of IDF (Israel Defence Force) operations against the terrorists of Hamas and other terror groups in the Gaza Strip," Prime Minister Benjamin Netanyahu said in a statement.
Washington has backed Israel's actions while France, Germany, and the United Nations urged restraint on both sides.
"We strongly condemn the continuing rocket fire inside of Israel and the deliberate targeting of civilians by terrorist organisations in Gaza," White House spokesman Josh Earnest said.