FN: An Israeli airstrike Sunday killed at least 56 Lebanese, mostly women and children, when it leveled a building where they had taken shelter. The deadliest attack in nearly three weeks of warfare forced U.S. Secretary of State Condoleezza Rice to cut short a Mideast mission and increased world pressure on the United States to back an end to the fighting.The stunning bloodshed pushed American peace efforts to a crucial juncture, as fury at the United States flared in Lebanon, which said it would no longer negotiate over a U.S. peace package without an unconditional ceasefire. U.N. chief Kofi Annan sharply criticized world leaders � implicitly Washington � for ignoring his previous calls for a stop.The attack in the village of Qana brought Lebanon’s death toll to more than 510. Throughout the day, workers pulled dirt-covered bodies of young boys and girls � dressed in the shorts and T-shirts they’d been sleeping in � out of the mangled wreckage of the three-story building.

Two extended families, the Shalhoubs and the Hashems, had gathered together for shelter from another night of Israeli bombardment in the border area when the 1 a.m. strike brought the building down.

“I was so afraid. There was dirt and rocks and I couldn’t see. Everything was black,” said 13-year-old Noor Hashem, who survived, although her five siblings did not. She was pulled out of the ruins by her uncle, whose wife and five children also died.

Israel apologized for the deaths but blamed Hezbollah guerrillas, saying they had fired rockets into northern Israel from near the building. Prime Minister Ehud Olmert said the campaign to crush Hezbollah would continue, telling Rice it could last up to two weeks more.

“We will not stop this battle, despite the difficult incidents this morning,” he told his Cabinet after the strike, according to a participant. “If necessary, it will be broadened without hesitation.”

The U.N. Security Council held an emergency meeting to debate a resolution demanding an immediate cease-fire � a step Washington has stood nearly alone at the council in refusing until the disarmament of Hezbollah is assured.

In a jab at the United States, Annan told the council in unusually frank terms that he was “deeply dismayed” his previous calls for a halt were ignored. “Action is needed now before many more children, women and men become casualties of a conflict over which they have no control,” he said.

After news of the deaths emerged, Rice telephoned Lebanese Prime Minister Fuad Saniora and said she would stay in Jerusalem to continue work on a peace package, rather than make a planned Sunday visit to Beirut. Saniora said he told her not to come.

Rice decided to cut her Mideast trip short and return to Washington on Monday morning.

British Prime Minister Tony Blair, who only days earlier gave his support to the U.S. stance, struck a more urgent note Sunday, saying Washington must work faster to put together the broader deal it seeks.

“We have to get this now. We have to speed this whole process up,” Blair said. “This has got to stop and stop on both sides.”

But Lebanon’s Saniora said talk of a larger peace package must wait until the firing stops.

“We will not negotiate until the Israeli war stops shedding the blood of innocent people,” he told a gathering of foreign diplomats. But he underlined that Lebanon stands by ideas for disarming Hezbollah that it put forward earlier this week and that Rice praised.

He took a tough line and hinted that any Hezbollah response to the airstrike at the village of Qana was justified. “As long as the aggression continues there is response to be exercised,” he said, praising Hezbollah’s leader Sheik Hassan Nasrallah.

Hezbollah said on its Al-Manar television that it will retaliate, vowing, “The massacre at Qana will not go unanswered.”

The largest toll from a single Israeli strike in past weeks was around a dozen � and Sunday’s dramatic deaths stunned Lebanese. Heightening the anger were memories of a 1996 Israeli artillery bombardment that hit a U.N. base in Qana, killing more than 100 Lebanese who had taken refuge from fighting. That attack sparked an international outcry that forced a halt to an Israeli offensive.

In Beirut, some 5,000 protesters gathered in downtown Beirut, at one point attacking a U.N. building and burning American flags, shouting, “Destroy Tel Aviv, destroy Tel Aviv” and chanting for Hezbollah’s ally Syria to hit Israel. Another protest by about 50 people on a road leading to the U.S. Embassy forced security forces to close the road there.

Images of children’s bodies tangled in the building’s ruins, being carried away on blankets or wrapped in plastic sheeting were aired on Arab news networks. The dead included at least 34 children and 12 women, Lebanese security officials said.

In Qana, Khalil Shalhoub was helping pull out the dead until he saw his brother’s body taken out on a stretcher. “Why are they killing us? What have we done?” he screamed.

Israel said Hezbollah had fired more than 40 rockets from Qana before the airstrike, including several from near the building that was bombed. Foreign Ministry official Gideon Meir accused Hezbollah of “using their own civilian population as human shields.”

It said residents of the village had been warned to leave, but Shalhoub and others in Qana said residents were too terrified to take the road out of the village. The road to the nearest main city, Tyre, is lined with charred wreckage and smashed buildings from repeated Israeli bombings.

More than 750,000 Lebanese have fled their homes in the fighting. But many thousands more are still believed holed up in the south, taking refuge in schools, hospitals or basements of apartment buildings amid the fighting � many of them too afraid to flee on roads heavily hit by Israeli strikes.

Lebanese Defense Minister Elias Murr disputed allegations that Hezbollah was firing missiles from Qana.

“What do you expect Israel to say? Will it say that it killed 40 children and women?” he told Qatar-based al-Jazeera TV station.

On Thursday, the Israeli military’s Al-Mashriq radio that broadcasts into southern Lebanon warned residents that their villages would be “totally destroyed” if missiles were fired from them. Leaflets with similar messages were dropped in some areas Saturday.

Israel on Sunday also launched its second significant ground incursion into southern Lebanon. Before dawn, Israeli forces backed by heavy artillery fire crossed the border and clashed with Hezbollah guerrillas in the Taibeh Project area, some three or four kilometers (1.8 to 2.5 miles) inside Lebanon.

Hezbollah said eight Israeli soldiers were killed. The Israeli military said only that four soldiers were wounded when guerrillas hit a tank with a missile.

Some 458 Lebanese, mostly civilians, had been killed in the campaign through Saturday, according to the Health Ministry � before the attacks on Qana. Thirty-three Israeli soldiers have died, and Hezbollah rocket attacks on northern Israel have killed 18 civilians, Israeli authorities said.

The U.N. World Food Program canceled an aid convoy’s trip to the embattled south after the Israeli military denied safe passage, the group said in a statement. The six-truck convoy had been scheduled to bring relief supplies to Marjayoun.

Many in the Arab world and Europe see the United States as holding the key to the conflict, believing that Israel would have to stop its offensive � sparked by Hezbollah’s July 12 abduction of two Israeli soldiers � if its top ally Washington insisted it had to.

The United States has balked at doing so, saying any cease-fire must ensure real and lasting peace.

Rice had come to the Mideast with a peace package that would call for the disarming of Hezbollah, release of Israel’s soldiers, deployment of a U.N.-mandated force in south Lebanon and the establishment of a buffer zone along the border.

Hopes had been raised earlier in the week when Hezbollah signed onto a Lebanese government peace plan that contained some similar items � though it left disarmament and deployment of the international force for later and dependent on conditions. Chief among those conditions was that Israel release Lebanese in its jails and agree to resolve a dispute over a piece of land it holds claimed by Lebanon.

Saniora said those idea still stand, but that Lebanon would not discuss them until the fighting stops.

Lebanese President Emile Lahoud lashed out at the United States, saying that if it was “serious, it can make Israel cease firing ….They (Americans) are still giving the green light to Israel to continue its aggression against Lebanon.”