JERUSALEM (AP) -- Palestinian militants barraged Israel with nearly 150 rockets on Thursday, killing three people as Israel pressed a punishing campaign of airstrikes on militant targets across the Gaza Strip. Three rockets struck the densely populated Tel Aviv area, and air raid sirens blared in the city as night fell.
The fighting, which has also killed 15 Palestinians in two days, showed no signs of slowing after dark. The attacks in the Tel Aviv area, some of the deepest rocket strikes on record, raised the likelihood of an even tougher Israeli response. Gaza militants launched the rocket barrage in retaliation for Israel's killing of the Hamas military chief in an airstrike on Gaza Wednesday.
Israeli Channel 2 TV showed panicked Tel Aviv residents running for cover and lying down on the ground after the air-raid sirens began sounding. The military said two rockets had been fired at the city, and residents heard an explosion. But there was no word on where they landed or reports of injuries. Police were exploring the possibility that the rockets landed in the sea.
Earlier in the day, a third rocket landed in an open area of Rishon Lezion, a city on Tel Aviv's southern outskirts, but there were no casualties.
Any attempt to disrupt life in Israel's business and cultural capital would mark a significant escalation by Gaza militants.
Defense officials say Israel is prepared to launch a ground invasion into Gaza if necessary. And Prime Minister Benjamin Netanyahu said the army was prepared for a "significant widening" of its Gaza 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 Defense 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 fighting, the heaviest in four years, has brought life to a standstill on both sides of the border, with schools canceled and people huddled indoors.
Israel and Hamas have largely observed an informal truce for the past four years. But in recent weeks, the calm unraveled in a bout of rocket attacks on Israel from Gaza and retaliatory Israeli airstrikes.
From Israel's perspective, Hamas escalated tit-for-tat fighting in recent days with a pair of attacks: an explosion in a tunnel along the Israeli border and a missile attack on an Israeli military jeep that seriously wounded four soldiers.
Israeli officials say they have not yet decided on whether to launch a ground invasion in Gaza, and it's not clear what would trigger it. But a strike on Tel Aviv itself, Israel's commercial and cultural capital, would mark a significant escalation.
While southern Israeli areas near Gaza have long coped with rocket fire, the attacks on the Tel Aviv area illustrated the significant capabilities that Hamas militants have developed. Gaza militants had previously hit Rishon Lezion before but never reached Tel Aviv, roughly 70 kilometers, or 50 miles, north of the strip.
Israel launched the offensive on Wednesday, killing the head of Hamas' militant wing and destroying dozens of rocket launchers. Israel has made special efforts to destroy launchers for Hamas' Iranian-made "Fajr" rockets, which are believed capable of flying even deeper into Israel.
Israel's military spokesman, Brig. Gen. Yoav Mordechai, said the air operation has delivered a "strong blow" to militants' launching sites.
In all, 15 Palestinians have been killed and nearly 200 wounded in fighting on Wednesday and Thursday. Three Israelis were killed earlier Thursday when a rocket struck an apartment building in the southern town of Kiryat Malachi. The Israeli military says three soldiers were wounded in a separate rocket attack.
The military said its air campaign has hit 230 targets across Gaza, and its "Iron Dome" rocket defense system has intercepted some 90 incoming rockets.
Still, Palestinian militants continued to launch rockets into Israel throughout the day.