Hamas has vowed revenge after an attempt to use Palestinian civilians as human shields resulted in several fatalities, as Israeli Air Force planes targeted the home of a Hamas commander.
Gazan emergency services claim Israeli strikes on Gaza killed 15 people on Tuesday and wounded 80 others, as the military began an aerial campaign against terrorists in the Strip and prepares for a potential ground offensive.
It was the most serious flare-up in and around the Islamist-controlled territory since November 2012, and came as Israel's cabinet reportedly authorized the army to call up 40,000 reservists for a possible assault on Gaza.
The deadliest single airstrike was on a house in the southern city of Khan Yunis belonging to a Hamas commander, killing seven people and wounding 25 others, medics said.
The attack "targeted the house of the al-Kaware family," emergency services spokesman Ashraf al-Qudra told AFP, saying children were among the injured.
The events leading up to the strike offer an insight into the difficulties facing IDF forces in combating Gaza-based terrorism. It also provides a revealing glimpse into the way Hamas and other terrorist groups violate international law through the use of human shields. Israeli leaders have in the past referred to such tactics as a "double war crime": firing missiles at Israeli civilians, while using Palestinian civilians as human shields.
Witnesses said an Israeli drone launched a warning flare prior to the strike, in a bid to allow innocent civilians to evacuate the area. Instead, relatives and neighbors gathered at the house to act as human shields, but shortly afterwards an F-16 fired a missile which leveled the building.
In response, Hamas said "all Israelis" would be potential targets for retaliation. "The Khan Yunis massacre... of children is a horrendous war crime, and all Israelis have now become legitimate targets for the resistance," spokesman Sami Abu Zuhri said on Facebook.
Hamas has repeatedly vowed to target Israeli civilians, including in a recent propaganda video aimed at the residents of the southern Israeli city of Beersheva.
Earlier, three terrorists were killed in a separate strike on a car in the Daraj neighborhood in the center of Gaza City, Qudra said.
Hamas's Al-Aqsa TV showed gruesome images of charred body parts being loaded onto ambulance stretchers.
Family members said all of them were Hamas militants, identifying one as Mohammed Shaaban, 32, a senior commander in Hamas's armed wing, the Ezzedine Al-Qassam Brigades. He was also head of the group's naval operations, they said.
Israel's army confirmed targeting Shaaban, describing him as "a senior Hamas operative".
In a separate strike near Nusseirat refugee camp, another man was killed, with witnesses telling AFP he was also a Hamas operative.
Later, two terrorists were killed Tuesday in a fresh Israeli air strike east of Gaza City, a spokesman for the emergency services said. Their identities have not yet been released.
"At least two people were killed and several wounded in an air strike on Shejaiya, east of Gaza City," Ashraf al-Qudra told AFP.
Hamas spokesman Sami Abu Zuhri warned Israel was "playing with fire" and would pay for its ongoing operations.
The deaths came hours after Israel announced the start of Operation Protective Edge, a military campaign aimed at stamping out rocket fire on southern Israel and destroying Hamas's military infrastructure.
Army figures show that since midnight, terrorists have fired 130 rockets at southern Israel, prompting the air force to strike 150 "terror targets" in Gaza.
Israel must 'wave the white flag'
Meanwhile, Hamas leader Ismail al-Askar, who serves as a "member of parliament" for the group's Gaza-based government, reiterated previous Hamas demands that the only way they would agree to stop the current barrage of rockets against Israeli civilians would be for Israel to agree to several conditions.
The first would be to end its air strikes against terrorists in Gaza, which he termed "aggression"; the second would be to end the limited blockade on the Strip, which Israel imposed to stop Hamas and other terrorist groups smuggling in weapons. The third condition, he said, was that Israel release the dozens of terrorists who were initially freed during the 2011 Shalit Deal, but rearrested during the IDF's recent operations in Judea and Samaria after they broke the terms of their release.
If not, Askar warned, Hamas was ready for a protracted war with Israel which could last months or even years.
"The resistance will not raise the white flag, and will not put down its weapons until the occupation waves the white flag and surrenders to the terms of the resistance.