JERUSALEM — The Israeli army said it launched an offensive operation early today against the Gaza Strip to quell rocket attacks, and a Palestinian official said Israeli airstrikes injured at least nine Palestinians.
The Israeli airstrikes come after Gaza militants fired dozens of rockets at southern Israel on Monday, setting off air raid sirens and forcing hundreds of thousands of Israelis to stay indoors.
The military rushed more forces to the border late Monday and had warned that such an offensive was likely.
A Twitter statement from the Israeli army said the offensive, dubbed "Operation Protective Edge," is intended to "stop the terror Israel's citizens face on a daily basis."
The army said it was carrying out airstrikes in the Gaza Strip early today. It did not elaborate.
Gaza health official Ashraf Al-Kedra said at least nine Palestinian civilians were brought to a Gaza hospital with light to moderate injuries from the airstrikes, including several who suffered from shock. He said some of the injured Palestinians were treated and released.
The latest violence came as Israel pressed forward with its investigation of six Jewish youths suspected of abducting and killing a Palestinian teenager, and Israeli leaders sought to calm an emotional debate over whether the country's politically charged atmosphere led to the gruesome crime. An Israeli official said three of the youths had confessed to the attack.
Tensions have been high since three Israeli teenagers kidnapped June 12 in the West Bank were later found dead, followed by last week's slaying of the Palestinian youth in what many suspect was a revenge attack. Throughout the unrest, Gaza militants have launched more than 200 rockets and mortars into Israel, including close to 100 on Monday alone.
Israel has responded with dozens of airstrikes, but has not been able to halt the attacks. Eight Palestinian militants were killed in fighting Monday, the highest death toll yet.
The army said at least 70 rockets were fired at Israel from Gaza on Monday, including 40 launched in a single hour after nightfall, setting off air raid sirens up to 50 miles from Gaza, the military said.
Twelve rockets were intercepted by rocket-defense batteries, it added, while the others landed in open areas. It was the deepest penetration of rocket strikes in the current round of fighting and raised the likelihood of an even tougher Israeli response.
Lt. Col. Peter Lerner, an Israel Defense Forces spokesman, had said the army was moving more infantry forces to the Gaza border and had received authorization to mobilize up to 1,500 reservists.
In Washington on Monday, State Department spokeswoman Jen Psaki said the U.S. condemns the rocket fire. "We also support Israel's right to defend itself against these attacks," she said.
During the day Monday, lines of Israeli tanks and buses were gathered near the border area as soldiers milled about. Late Monday, with roads in southern Israel all but empty, a flatbed truck carrying an armored vehicle made its way toward the border area.
Israel has launched two broad military operations in Gaza in the past five years, most recently in 2012, when eight days of heavy fighting ended in an Egyptian-mediated truce.
The increased rocket fire followed the killing of Mohammed Abu Khdeir, a 16-year-old Palestinian boy from east Jerusalem who was abducted and burned to death last week.
Israeli officials Sunday announced the arrests of six Jewish youths in the killings.
Abu Khdeir's death triggered several days of violent protests in Arab areas of Jerusalem and northern Israel as Palestinians accused Israeli extremists of killing the boy to avenge the earlier deaths of the Israeli teens.
The news that the suspects were Jewish set off nationwide soul-searching over how Israelis could possibly carry out such a gruesome crime. A preliminary autopsy found that Abu Khdeir was still alive when he was set on fire.
"I am ashamed on behalf of my nation and grieve with you," President Shimon Peres told Abu Khdeir's father, Hussein, in a phone call. "The only thing left for all of us to do is to ensure that no more children are murdered, and no more tears are shed by mothers."
Peres, a Nobel Peace laureate, was among top Israeli officials, including Prime Minister Benjamin Netanyahu, who reached out to the family.
Netanyahu, who has condemned Abu Khdeir's death and tried to calm the public, said he had expressed his condolences.
"I would like to express my outrage and that of the citizens of Israel over the reprehensible murder of your son," a statement quoted Netanyahu as saying.
Rachelle Fraenkel, the mother of one of the slain Israeli teenagers, said that even from the "abyss" of her own pain, she could not describe her distress over the killing of the Arab boy.
"No mother and father should endure what we are going through now," she said.