The White House says the U.S. strongly condemns the barrage of rocket fire from Gaza into Israel and regrets the loss of life.
Spokesman Jay Carney says there is "no justification" for the violence perpetrated by Hamas and other terrorist organizations. And he called on those responsible to immediately stop the "cowardly acts."
Carney says that while Hamas claims to have the best interests of the Palestinian people at heart, the violence it continues to engage in is counterproductive to the Palestinian cause.
Palestinian militants launched nearly 150 rockets at Israel on Thursday, killing three people. Israel launched its own offensive Wednesday, killing the head of Hamas' militant wing Aha Jab and destroying dozens of rocket launchers. Hamas vows to avenge his death.
"The blood of our leader will be the fuel of our resistance. Israel is wrong if they think that this will be the end of Hamas," said Fawzi Barhoum.
There are more deaths on both sides of the border, and Israel's military is warning they have not ruled out a possible ground campaign in Gaza.
Palestinians say so far, 13 people have been killed in Gaza, including two children.
The Israeli army says a rocket has reached the southern outskirts of Tel Aviv, by far the farthest strike by Gaza militants in two days of fighting.
The military said the rocket landed in Rishon Lezion, a city just south of Tel Aviv located in heavily populated central Israel.
The rocket landed in an open area and caused no damage or injuries. Nonetheless, it illustrated the growing capabilities of Gaza militants.
The Israeli military launched an offensive on Wednesday, in large part to take out rocket launchers.
Israel's military spokesman, Brig. Gen. Yoav Mordechai, says the air operation has delivered a "strong blow" to militants' launching sites.
Overnight Palestinian rockets have continued to fall in Israel, one hitting an apartment block killing three Israelis.
All morning, residents heard the thump and and saw the thick black smoke of Israeli airstrikes.
"No government would tolerate this 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," said Benjamin Netanyahu, Israeli prime minister.