JERUSALEM — An Israeli soldier was killed in a ground operation in the Gaza Strip Friday, the military said. The circumstances of his death were not immediately clear.
Israel’s chief military spokesman Brig. Gen. Motti Almoz told Israeli Army Radio ‘‘we are checking the circumstances’’ behind the soldier’s death.
It was the first military casualty since Israel announced the start of a ground operation into Gaza.
Tanks rolled into the northern Gaza Strip Thursday night and naval gunboats pounded targets in the south as Israel began a ground invasion after 10 days of aerial bombardment failed to stop Palestinian militants from showering Israeli cities with rockets.
Israeli leaders said the incursion was a limited one focused on tunnels into its territory like the one used for a predawn attack Thursday that was thwarted. They said it was not intended to topple Hamas, the militant Islamist movement, from its longtime rule of Gaza.
As rockets continued to rain down on Israeli cities, a military spokesman said the mission’s expansion was “not time bound” and was aimed to ensure Hamas operatives were “pursued, paralyzed and threatened” as it targeted “terrorist infrastructure” in the north, south and east of Gaza “in parallel.”
As midnight approached Thursday, residents of some sparsely populated farmland in northern Gaza were cowering in their homes, afraid to answer mobile phones or peek out windows. Some sent text messages reporting that they could hear tank shelling, heavy artillery, and F-16s dropping bombs. Moussa al-Ghoul, 63, who lives northwest of Beit Lahiya, said his neighborhood had turned into “a war zone” with tanks surrounding his home, having destroyed those of two of his sons. He said shells were landing “everywhere.”
Gaza news outlets reported that electricity had been cut to 80 percent of the coastal territory after cables bringing power from Israel were damaged.
After the early-morning tunnel episode, the day settled into an extended calm as both sides abided a United Nations request for a five-hour humanitarian pause in the fighting. But by 3 p.m., the violence roared back as the Palestinian death toll neared 250 and more than 120 rockets rained on cities throughout southern and central Israel all afternoon and evening.
“We will strike Hamas and we are determined to restore peace to the state of Israel,” the military spokesman, Lt. Col. Peter Lerner, told reporters in a conference call. “It will progress according to the situation assessment and according to our crafted and designed plan of action to enable us to carry out this mission.”
Watch: IDF briefing
Israel began to draft 18,000 reservists, adding to 50,000 already mobilized in recent days; Lerner said the ground forces would include infantry and artillery units, armored and engineer corps, supported by Israel’s “vast intelligence capabilities,” air force and navy.
Fawzi Barhoum, a spokesman for Hamas, called the invasion “a dangerous step.”
“The occupation will pay its price expensively,” he said in a statement, referring to Israel, “and Hamas is ready for confrontation.”
Prime Minister Benjamin Netanyahu of Israel did not make a public statement Thursday night, but several of his ministers said on television that a unanimous Cabinet had authorized Netanyahu and the defense minister a few days ago to send in ground troops when they deemed necessary.
“With a heavy heart we embarked on this operation, in order to destroy the tunnels, as just this morning we have seen their deadly potential,” said Naftali Bennett, the economy minister and leader of the right-wing Jewish Home party. “Difficult days are ahead of us,” he added. “We are also operating against the rockets and all of the existing threats, but the No. 1 target is the tunnels.”
Israel did not send ground troops into Gaza during eight days of cross border violence in 2012. It was condemned internationally for an intense three-week air-and-ground campaign in 2008-09, when 1,400 Palestinians were killed along with 13 Israelis in fierce street fighting. Israel originally seized the territory in the Six-Day War in 1967 and evacuated its settlers and soldiers in 2005, but maintained restrictions on imports, exports and travel for the Palestinians left behind.
The military operation started about 10 p.m., hours after Israel bombed a rehabilitation hospital and another airstrike killed four children playing on a Gaza City rooftop — an echo of the previous day’s bombing that left four young children, all cousins, dead on a beach.
At the Al-Wafa Rehabilitation Hospital in Gaza City, most but not all of the 17 patients and 25 doctors and nurses were evacuated before the electricity was cut and heavy bombardments nearly destroyed the building, doctors said.
“We evacuated them under fire,” said Dr. Ali Abu Ryala, a hospital spokesman. “Nurses and doctors had to carry the patients on their backs, some of them falling off the stairway. There is an unprecedented state of panic in the hospital.”
Along the Gaza City seafront, as tanks entered the north, there was a near-constant staccato of gunboats firing in bursts of five blasts each, sending flashes above the dark water. They were shelling a target south of Gaza’s port, the red lights of their barrels visible from shore, the impact of their artillery echoing a second later. Earlier, warplanes whooshed over the city as they have for more than a week, and the high-pitched hum of drones could be heard over the call to prayer from mosques to end the daily fast during the Muslim holy month of Ramadan.
“Communications with Gaza have become problematic” since the ground invasion, said a statement from Christopher Gunness of the United Nations Relief and Works Agency, which provides health care, education, and other services for the more than half of Gaza’s 1.7 million residents, who are classified as Palestinian refugees. The agency is currently sheltering thousands who evacuated their homes. “We urgently appeal for restraint so that civilians who have suffered enough in this appalling conflict do not suffer further,” Gunness said.
Brig. Gen. Moti Almoz, chief spokesman of Israel’s military, said on television: “I will now, uncharacteristically, ask the residents of Gaza to move away from the areas our forces are operating in — they are operating with extreme force.”
The United Nations estimates that about three-quarters of those killed so far were civilians, not militants, and about 50 of them children. Palestinian health officials said at least 17 youths died in airstrikes Wednesday and Thursday, raising sharp new questions about civilian deaths.
Relatives collapsed in grief around sunset at Shifa Hospital, where the four children who had been killed on the rooftop — twin brothers Jihad and Wissam Shuheiber, 8; their cousin Afnan, 10; and a friend, Yassin Al-Himidi, 4 — laid on a single table in the morgue, their bodies deceptively intact. One of the boys wore only his underpants, decorated with superheroes.
The military, which on Wednesday issued a statement describing bombing on the beach bombing that also killed children as having a “tragic outcome,” declined to offer an explanation for Thursday’s 6 p.m. strike on the Gaza City rooftop. Israeli officials say they take precautions to avoid hitting civilians but that Hamas makes it hard by firing rockets from residential areas and discouraging residents from evacuating their homes.
“We don’t need statements of regret from Israel,” Peter Bouckaert of Human Rights Watch said in a Twitter message. “We need investigation and an end to the killing.”
It had been a roller-coaster day, starting with Israel’s early-morning report that it had foiled the attack through the tunnel at about 4:30 a.m. by striking from the air at 13 Palestinians who emerged from it and tried to infiltrate a kibbutz, the first time that had happened in the current conflagration. Lerner said later that the incursion “illustrates the clear and immediate threat we have from the Gaza Strip,” and noted that Israel had uncovered four similar tunnels into its territory over the last 18 months.
PHOTOS: Israel-Hamas attacks
The humanitarian pause urged by the United Nations started at 10 a.m., and Gaza residents filled the streets, shopping for food and toys and crowding cash machines open for the first time since the operation began. But the lull was pierced around noon by a brief flurry of mortars fired from Gaza, with rockets fired toward Israel precisely at 3 p.m., the designated endpoint of the lull. The strikes continued through the afternoon and evening.
Israel shot down a drone near Ashkelon, not far from its border with Gaza, the second unmanned aerial vehicle sent aloft by Gaza this week.
At one point, there was word from Egypt that an agreement had been reached for a cease-fire starting at 6 a.m. Friday. Instead, the violence only increased.
“We have to look at this as an operation in stages: its first stage was attacks from the air and sea, and this is the second stage, where we reach contact with the Hamas,” Eli Marom, commander of Israel’s navy from 2007 to 2011, said on Israel’s Channel 2 News. “You have to understand this is a long campaign. This is only its second stage, and there can be other stages.”
Michael B. Oren, Israel’s former ambassador to Washington, said in a late-night interview that Netanyahu had “exercised extraordinary restraint up until now” by not engaging ground troops and “paid a heavy political price for it.” Thursday’s tunnel attack, he said, “was a game changer,” adding: “Essentially, Hamas invaded Israel first.”
In contrast to the Iron Dome missile-defense system that Israel says has stopped some 300 rockets from hitting populated areas over the last 10 days, Oren said, “We don’t have a response to the tunnels.”
He added, “They are reinforced concrete tunnels, basically impregnable from the air and their openings are camouflaged.”
Amos Yadlin, director of Israel’s Institution for National Security Studies and former chief of military intelligence, similarly said in a radio interview earlier Thursday that the tunnel attack “clarified to those who were still wondering if it was right to conduct a ground move against certain points.”
A senior Israeli military official put it this way at a recent briefing, “Actually there are two Gazas: one above the ground and another under the ground.”