By Jethro Mullen, Steve Almasy and Ben Wedeman
GAZA CITY (CNN) -- Israel was attacked from a second front Friday, but it is unlikely that a rocket fired from Lebanon signifies the widening of a conflict that has left at least 100 dead in Gaza.
The rocket launched from Lebanon landed near the northern Israeli town of Metula, which sits right by the Lebanese border, and no damage or injuries have been reported. It was not immediately clear who fired the rocket.
An Israel Defense Forces spokesman said Israel holds the Lebanese government responsible for the attack, but concerns that Israel will face a two-front conflict are unlikely to be realized.
Hezbollah, which operates in Lebanon and is caught up in other conflicts in the region, probably does not have the appetite to start a war with Israel.
Nonetheless, Israel responded with artillery that landed in the vicinity of the Lebanese town of Kfar Shouba. No casualties were reported, the Lebanese army said.
Israel continued to weather rocket attacks by the Palestinian group Hamas in Gaza, but virtually all of the casualties in the conflict have been suffered on the Gazan side.
Though menacing, nearly all the Hamas rockets have been intercepted by the Israeli air defense system or struck empty areas. Airstrikes by Israel in Gaza, in contrast, have been blamed for at least 100 deaths, including 22 children and 20 women, a spokesman for Gaza's Ministry of Health said.
Israel calls up reservists
As fears of an Israeli ground assault grew among Gaza residents Thursday, Israel revealed it has beefed up its forces by calling about 30,000 reservists to their units.
"We are utilizing that force to enable us to create a substantial force around Gaza, that if it is required, we'll be able to mobilize as soon as possible," Israel Defense Forces spokesman Peter Lerner told CNN's Wolf Blitzer.
The Israeli Cabinet has authorized the military to call up 40,000 troops if needed. That is 10,000 more than were called up during Israel's offensive into Gaza in November 2012.
Government spokesman Mark Regev said units have been deployed.
"We're ready to go, if we need to go," he told Blitzer.
Regev said Israel didn't want a situation where Hamas, which controls Gaza, was given a "timeout" where it could regroup before restarting its attacks.
Gaza toll rises
Hamas' military wing, meanwhile, said in a video statement late Thursday that it was ready for an extended confrontation.
"We assure the enemy that we have prepared ourselves for a very long battle, not for a week or 10 days as described by some of the enemy's commanders, but for very long weeks," the speaker said in the video, wearing camouflage fatigues with most of his face covered by a scarf.
"The world will see the skulls of your soldiers being stepped on by Gaza's children with their bare feet," the speaker said.
The mood is grim in Gaza, where, in addition to the deaths, Israeli airstrikes have injured more than 650 people since they began late Monday, according to Palestinian officials.
Throughout Gaza, people are expecting an Israeli ground incursion. Many people have nowhere to flee and there are no bomb shelters.
"I can't leave. I have nowhere to go. Better to stay at home, inside and be safe," one resident of the town of Bait Hanoun in northern Gaza told CNN.
Most residents live in homes without safe rooms and walls made of breeze block, which a bullet could pass through like paper.
Children among dead
Each day, the death toll has risen in Gaza. The Israel Defense Forces said Thursday it has struck at 785 Hamas targets since announcing the start of its offensive Monday with the aim of hurting Hamas and stopping rocket attacks on Israel.
Tensions in the region flared last week after the killings of three Israeli teenagers in the West Bank, followed by the killing in Jerusalem of a Palestinian teenager that police say may have been an act of revenge. Israel blames Hamas for the deaths of the three Israeli youths, although the group has denied responsibility.
The IDF has said its targets in Gaza include rocket launchers, tunnels and the homes of senior Hamas leaders, which the IDF describes as "command centers."
But among the dead are an 18-month-old baby and an 80-year-old woman, according to information from the Palestinian Health Ministry.
The Palestine Liberation Organization said Israeli bombs have hit civilian infrastructure, including a line that provides water to a refugee camp and a sewage plant.
The IDF has not responded to the accusations. It says it uses phone calls and drops empty shells on roofs -- what it calls "roof knocking" -- to warn civilians that airstrikes are imminent. But the approach doesn't guarantee their safety.
U.S. willing to help broker cease-fire
Hopes for a cease-fire appeared dim even as world leaders called for the two sides to stop the violence.
U.S. President Barack Obama and Israeli Prime Minister Benjamin Netanyahu spoke by phone.
"The United States remains prepared to facilitate a cessation of hostilities, including a return to the November 2012 cease-fire agreement," the White House said in a written statement, referring to the Egyptian-brokered deal that halted the previous Israel-Hamas conflict.
The President also condemned rocket attacks from Gaza and said the United States reaffirmed Israel's right to defend itself.
U.N. Secretary General Ban Ki-moon told reporters he has been reaching out to regional leaders in an attempt to help get the two sides to stop the violence soon.
"It is imperative not only to restore calm today, but to establish a political horizon for tomorrow," he said. "Without the prospect of an end to the conflict, the sides will grow ever more polarized."
'Prepared for all possibilities'
There have been hints for days from some Israeli officials about the possibility of a ground offensive in Gaza, but there were questions about the government's appetite for such a conflict.
Netanyahu said Wednesday that the aerial offensive would be expanded and continue "until the firing at our communities stops and quiet is restored."
He didn't specify what the expansion of Operation Protective Edge would entail, saying that Israel's military "is prepared for all possibilities."
No Israelis have been killed so far by the hundreds of rockets fired toward southern Israel by Hamas, Islamic Jihad and other militant groups in Gaza. Some Israelis have been wounded by the attacks.
The Israel Defense Forces said Friday that since the start of Operation Protective Edge, more than 570 rockets have been fired at Israel. The country's Iron Dome defense system has intercepted more than 100 of them, the IDF said.
Hamas and other militant groups in Gaza are believed to have about 10,000 rockets of varying ranges, according to the Israeli military. Israel has said some 3.5 million residents live in areas within reach of the rockets.
Sides speak at U.N. Security Council meeting
Israel and the Palestinians laid out their positions at a U.N. Security Council meeting Thursday.
Ambassador Riyad Mansour, permanent observer of the State of Palestine to the United Nations, accused Israel of "terrorizing our people, killing dozens of civilians and injuring hundreds."
Allegations by Israel that Palestinians are using human shields are "audacious," he said, and he rejected the argument that Israel is defending itself.
Israel "deliberately carries out reprisals and collective punishment against the Palestinian people in declared retaliation and revenge ... for the killing of the three Israeli settlers, which the Palestinian leadership has clearly condemned," Mansour said.
Israel, for its part, called on the Security Council to condemn Hamas and its launching of rockets across the border.
Ron Prosor, Israeli ambassador to the United Nations, played a recording of a siren during the middle of his remarks, to show how Israelis only have 15 seconds, he said, to run for cover.
"Asking Israel to show restraint while our cities are under constant attack is like asking the fire brigade to battle an inferno with nothing more than buckets of water," he said.
CNN's Ben Wedeman reported from Gaza City. Jethro Mullen reported and wrote from Hong Kong, and Steve Almasy reported and wrote from Atlanta. CNN's Michael Pearson, Yousuf Basil, Nada Husseini, Brian Walker, Larry Register, Kareem Khadder, Diana Magnay, Tal Heinrich, Amir Tal, Salma Abdelaziz and Talal Abu Rahma contributed to this report.
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