By Jodi Rudoren and Anne Barnard

New York Times News Service

JERUSALEM — Israeli tanks rolled into the northern Gaza Strip on 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, such as the one used Thursday for a predawn attack, which 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 observed 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.”

Israel began to call up 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 seized the territory in the 1967 war 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, which left four young children, all cousins, dead on a beach.

The United Nations estimates that about three-quarters of those killed have been civilians, not militants, and about 50 of those were children.

Palestinian health officials said at least 17 children died in airstrikes Wednesday and Thursday, raising sharp new questions about civilian deaths.