JERUSALEM — The Israeli military launched what could be a long-term offensive against the Hamas-ruled Gaza Strip on Tuesday striking at least 50 sites in Gaza and mobilizing troops for a possible ground invasion aimed at stopping a barrage of rocket attacks against Israel.
The military said "Operation Protective Edge" looks to strike the Islamic Hamas group and end the rocket fire that has reached deeper into Israel and intensified in recent weeks amid tensions over the killing of three Israeli teenagers and the apparent revenge killing of a Palestinian teenager.
In a statement, the military said it was seeking to "retrieve stability to the residents of southern Israel, eliminate Hamas' capabilities and destroy terror infrastructure operating against the State of Israel and its civilians."
Nearly 300 rockets and mortars have been fired at Israel in recent weeks, including a barrage of close to 100 projectiles on Monday alone, the military said, a huge surge after years of relative quiet that followed a previous Israeli campaign to root out Gaza rocket launchers.
"We have repeatedly warned Hamas that this must stop and Israel's defense forces are currently acting to put an end of this once and for all," said Mark Regev, a spokesman for Prime Minister Benjamin Netanyahu.
Israel has responded with dozens of airstrikes, and eight Palestinian militants were killed Monday. Israel had signaled that it would not launch a larger offensive if the militant group Hamas ceased the rocket fire.
"They chose the direction of escalation," said military spokesman Lt. Col. Peter Lerner, in a telephone briefing to reporters. "So the mission will go on as long as we feel it is necessary to carry it out. We don't expect it to be a short mission on our behalf."
After a brief early morning lull, the rocket fire from Gaza resumed Tuesday with more than 15 rockets fired toward southern Israel, including the cities of Ashdod and Ashkelon. The Associated Press video showed launches from inside Gaza.
The military said five were intercepted by the country's sophisticated Iron Dome missile defense system. A German cruise operator docking in the Ashdod port said debris fell onto one of its ships late Monday as it was departing.
None of the 2,700 vacationers and crew aboard the AIDAdiva was harmed. "However, small debris that according to experts could have come from a defense missile were found on the passenger deck," the company said. The ship continued to Crete without delay.
Israel's defense minister announced a special state of emergency in the region Tuesday as summer camps and kindergartens were shut down and residents were encouraged to stay close to their homes.
Among the 50 sites the military said it targeted early Tuesday were four houses it said were "activity sites" belonging to Hamas militants involved in launching rockets at Israel or other militant activity. There were no reported casualties in the strikes.
The military identified the men whose houses were targeted as Eiad Sakik, Abdullah Hshash, Samer Abu Daka, and Hassan Abdullah. The Associated Press filmed Abu Daka and Abdullah's demolished homes in the Khan Younis area of the Gaza Strip.
In addition, the military said it struck three militant compounds, 18 concealed rocket launchers, and other militant infrastructure sites. Most were targeted in airstrikes, and three were attacked from the sea.
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.
Lerner, the military spokesman, said the army will gradually increase its attacks on Hamas in Gaza, and is recruiting additional reservists for a potential ground invasion of Gaza.
Hamas has amassed about 10,000 rockets, including longer-range rockets that can reach "up to Tel Aviv and beyond," Lerner said, adding that the military was preparing for the possibility that Hamas would launch rockets toward Israel's heartland and its commercial and cultural hub.
The military ordered hundreds of thousands of Israelis within a 40-kilometer (25-mile) radius of the Gaza Strip, including Israelis in the major southern city of Beersheva, to stay indoors and near shelters.
Lerner said last month's kidnapping and killing of three Israeli teenagers in the West Bank was connected to the intensified rocket fire carried out by Hamas militants in Gaza. Israel blames Hamas for the teens' abduction and is conducting a manhunt for two Hamas-affiliated Palestinians in the West Bank it believes carried out the kidnapping and killing.
The Israeli government has not yet provided proof of Hamas' involvement in the kidnapping.
"The abduction of the three boys only cost them, and they had no gains from it," Lerner said. "Therefore they have increased their involvement in rocket fire," adding that nearly all of the rocket fire at Israel Monday was carried out by Hamas, not militants affiliated with other groups. He said Hamas was "trying to gain clout."
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.
The charged climate inspired President Barack Obama to pen an op-ed for the Israeli newspaper Haaretz.
"All parties must protect the innocent and act with reasonableness and restraint, not vengeance and retribution," Obama said in the piece published Tuesday.
Obama warned of a "dangerous moment" for the region after the collapse of U.S.-backed peace talks.
"As I said last year in Jerusalem, peace is necessary, just, and possible. I believed it then. I believe it now," he wrote. "Peace is necessary because it's the only way to ensure a secure and democratic future for the Jewish state of Israel."