The escalating conflict between Israel and Gaza threatens to spiral further out of control after a rocket fired from Gaza reportedly landed in the sea close to Tel Aviv, in a sign that Palestinian militant groups could be deploying long-range weapons from their stockpiled arsenals.
In a second day of intense bombardment of Gaza and a continuing barrage of rocket fire into Israel, sirens were activated in Tel Aviv for the first time since the 1991 Gulf war to warn residents to take shelter. Israeli television showed panicked residents running for cover when the air-raid sirens sounded.
The militant group Islamic Jihad claimed responsibility for firing a Fajr 5 rocket at the city. "We have widened the range of the battle to reach Tel Aviv and what is coming will be greater," the group said in a statement.
Earlier another rocket struck close to the city of Rishon Lezion, 22 miles north of Gaza. The Israeli military said nearly 150 rockets were fired from Gaza on Thursday, one of which struck an a block of flats, killing three residents and wounding three children.
In Gaza, bombardment continued for a second day, with Israeli planes targeting militants and weapons sites. But there was mounting concern about rising civilian casualties, with the Gaza ministry of health reporting that four children and a woman pregnant with twins were among the dead. It said 130 people had been wounded.
Hamas and Israel declared states of emergency.
Israeli troops were reported to be moving south in preparation for a possible ground invasion of Gaza. However, the IDF spokeswoman, Avital Leibovitch, indicated that such a move was not imminent, saying it was only an "option" and ground forces were "on alert".
One trigger for an order to launch a ground offensive could be a rocket landing in Tel Aviv, Israel's second-largest city. Gaza's militants have never reached the city, which is roughly 50 miles north of the strip.
The city of Tel Aviv has a resident population of more than 400,000, but hundreds of thousands of more live in the surrounding area or commute to work there. The Israeli military has its headquarters in the city.
The Israeli prime minister, Binyamin Netanyahu, told a press conference the army was preparing for a "significant widening" of its offensive.
"No government would tolerate a situation where nearly a fifth of its people live under a constant barrage of rockets and missile fire, and Israel will not tolerate this situation," he said.
"This is why my government has instructed the Israeli Defence Forces to conduct surgical strikes against the terrorist infrastructure in Gaza.
"And this is why Israel will continue to take whatever action is necessary to defend our people." The military had been instructed to avoid targeting civilians, he added.
In a sign that the conflict is straining the Jewish state's fragile relations with its long-time ally Egypt, an Egyptian delegation, led by the prime minister, Hisham Kandil, is expected to visit Gaza on Friday in an act of solidarity with the Palestinians.
President Mohamed Morsi said Israel's military assault was "unacceptable", and the Muslim Brotherhood, with which he has strong ties, called on Egypt to sever diplomatic relations.
A visit to Gaza by Egyptian officials would signal a significant worsening of relations between the two allies, and would renew fears that the post-revolution government in Cairo may review its 33-year-old peace treaty with Israel.
"Prime Minister Hisham Kandil will visit, along with security officials, the Gaza Strip on Friday for a day's visit to meet with officials there and show solidarity with the Palestinian people," an Egyptian cabinet official told Reuters news agency.
The delegation may include Egypt's intelligence chief, General Mohamed Raafat Shehata, as well as the prime minister, according to the Reuters report.
The Muslim Brotherhood, to which Morsi has close ties, has called for a "Day of Rage" in Arab capitals on Friday. The Brotherhood has strong ideological links with Hamas.
Egypt recalled its ambassador to Israel on Wednesday in protest at the Israeli air strikes on Gaza.
Jordan, another ally of Israel, also condemned the escalating violence along with Qatar, Iran and Syria.
The United States criticised Hamas, with Mark Toner, deputy state department spokesman, saying there was "no justification for the violence that Hamas and other terrorist organisations are employing against the people of Israel".
The French foreign minister, Laurent Fabius, said: "It would be a catastrophe if there is an escalation in the region.
"Israel has the right to security but it will not achieve it through violence. The Palestinians also have the right to a state."
