Israel has killed the leader of the Hamas military wing in a surgical missile strike in Gaza that could result in a fresh war in the region.
Ahmed Jabari, 46, the head of the Islamist group's military arm, the Izz ad-Din al-Qassam, died as he travelled by car with another senior Hamas leader in the Palestinian city.
Three Palestinians were killed in another Israeli strike on Thursday morning, the BBC has reported.
Hamas has said that Israel will "pay a high price" for the attack, according to the New York Times, while Izz ad-Din al-Qassam posted a message on its Twitter profile warning that the strike had opened the gates of hell.
The Palestinian envoy to the United Nations Riyad Mansour said at least nine people have been killed in Israeli air strikes.
The Israeli Defence Force (IDF) launched the attack as part of Operation Pillar Of Defense and described Jabari in a statement as "a senior Hamas operative who served in the upper echelon of the Hamas' command and was directly responsible for executing terror attacks against the State of Israel in the past number of years".
The IDF said: "The purpose of this operation was to severely impair the command and control chain of the Hamas leadership, as well as its terrorist infrastructure. This was a surgical operation in cooperation with the Israeli Security Agency, that was implemented on the basis of concrete intelligence and using advanced capabilities.
"The IDF will continue to target sites that are used for carrying out terror attacks against the citizens of Israel while improving their daily security."
Jabari has long been a key target for the IDF, and topped Israel’s most-wanted list for his apparent involvement in a string of attacks against Israel, including co-ordinating the capture of soldier Gilad Shalit in 2006, who was held hostage in Gaza for more than five years.
The Guardian reported that on Tuesday Israeli prime minister Binyamin Netanyahu told mayors of towns near the Gaza border: "Whoever thinks that they can damage the daily lives of residents of the south, and that they won't pay a heavy price for this, they are mistaken."
After the strike, Netanyahu said in a press statement: "Hamas and the terror organizations have elected in recent days to escalate their attacks on Israel's citizens.
"We are not prepared to make peace with a situation in which Israel's citizens are menaced by the terror of rocket fire. No country would agree to such a situation; Israel is not prepared to reconcile itself to such a situation.
"Today we have damaged the strategic targets of Hamas in a precise fashion; we have substantially damaged the launch capabilities of rockets from Gaza to central Israel and we are damaging the launch capability to Southern Israel.
"The terror organizations hurt our citizens with premeditation, while they deliberately conceal themselves behind their own citizens.
"We in contradistinction refrain to the extent possible from harming civilians; this is a fundamental difference between us and them. They would simply like to wipe us off the face of the earth and they have no reservations about harming innocent civilians.
"Today we transmitted a clear message to the Hamas organization and to other terrorist organizations and should the need arise, the IDF is prepared to expand the action. We will continue doing everything to protect our citizens."
The sound of gunfire could be heard echoing throughout Gaza following the missile strike with Hamas spokesman Taher Anunu telling BBC Arabic: "This was a heinous crime that will have repercussions."
Reuters reported Ismail Haniyeh, the prime minister of Hamas’s Gaza government, saying in a statement: “We call on our Arab brothers, and especially Egypt ... and the new Egyptian presidency, to suppress this barbaric campaign in defense of Gaza and its people."
“I call for an urgent Arab summit to confront the brutal aggression,” he added.
Palestinian negotiator Saeb Erekat told Al Jazeera the assassination of Jabari is “a major escalation against our people in Gaza… We hold the Israeli government responsible."
The Jerusalem Post reported that militants in Gaza have launched at least 55 rockets into southern Israel following the assassination, but most have been deflected by the Israeli military.
The Post said six rockets landed near the town of Beersheba and one rocket struck a house in Ashdod, another damaged electric infrastructure in Eshkol.
The Foreign Office has called on Hamas and Israel "to exercise restraint to prevent a dangerous escalation".
Meanwhile, Noam Shalit, the father of Gilad Shalit, who was abducted by Hamas in 2006, urged the Israelis to consider dialogue with the extremist group, according to Haaretz Newspaper journalist Barak Ravid:
Amnesty International Middle East and North Africa Deputy Director Ann Harrison called for restraint from all sides.
She said: “All sides have to step back from the brink in order to protect civilian lives.
“The Israeli military must not carry out further indiscriminate attacks, or attacks in densely-populated residential areas that will inevitably harm civilians.
“Palestinian armed groups in Gaza meanwhile must not fire indiscriminate rockets into Israel. The international community must put pressure on both sides to fully respect the laws of war and protect civilian lives and property.”
Egyptian President Mohammed Mursi has recalled the ambassador to Israel and summoned Israel’s ambassador in Cairo, calling for an "immediate halt to the attacks."
In the wake of the attack, the IDF launched a social media offensive, warning other Hamas leaders they too were targets, and live-tweeting attacks from both sides.