Beirut, Lebanon Israel massed tanks and troops on the border, called up reserves and warned civilians to flee Hezbollah-controlled southern Lebanon as it prepared Friday for a likely ground invasion.
The Israeli army confirmed some of its troops have been operating in Lebanon for days although no major incursion has been launched.
An official from the U.N. monitoring force in south Lebanon, speaking on condition of anonymity because he was not authorized to talk to the press, told The Associated Press in Beirut that between 300 and 500 troops are believed to be in the western sector of the border, backed by as many as 30 tanks.
Israeli forces would conduct ground operations as needed in Lebanon, but they would be "limited," Israeli army chief of staff Lt. Gen. Dan Halutz said. He also said nearly 100 Hezbollah guerrillas have been killed in the offensive in Lebanon.
"We will fight terror wherever it is because if we do not fight it, it will fight us. If we don't reach it, it will reach us," Halutz said at a news conference in Tel Aviv. "We will also conduct limited ground operations as much as needed in order to harm the terror that harms us."
Israeli will allow aid supplies into Lebanon, an envoy said, a day after the United Nations warned of a growing humanitarian crisis following 10 days of the heaviest bombardment of the country in 24 years.
Hezbollah militants fired 11 rockets at Israel's port city of Haifa, wounding five. Israeli warplanes pounded the Beirut-to-Damascus highway, collapsing part of Lebanon's longest bridge. A U.N.-run observation post near the border was hit, but no one was hurt.
Ships lined up at Beirut's port as a massive evacuation of Americans and other foreigners picked up speed. U.S. officials said more than 8,000 of the roughly 25,000 Americans in Lebanon will be evacuated by the weekend.
As sunset approached, lines of tanks, troops, armored personnel carriers and bulldozers were parked on a two-lane highway in northern Israel -- close enough for some soldiers to see Lebanese villages and homes.
A senior Israeli military official said it intends to destroy Hezbollah's tunnels, hideouts, weapons caches and other assets during its expected land incursions into southern Lebanon, not create a buffer zone as it did during its 1982-2000 occupation.
The goal is to weaken Hezbollah so that the Lebanese army can move into areas previously controlled by the guerrillas, possibly with the aid of an increased international peacekeeping force, said the official, speaking on condition of anonymity because the topic dealt with sensitive military matters.
Mounting civilian casualties and the displacement of hundreds of thousands of Lebanese could limit the time Israel has to achieve its goals, as international tolerance for the bloodshed and destruction runs out.
An Israeli military radio station warned residents of 12 border villages in southern Lebanon to leave before 2 p.m. Friday.
At least 335 people have been killed in Lebanon in the Israeli campaign, according to the Lebanese health minister. Thirty-four Israelis also have been killed, including 19 soldiers.
Al-Arabiyah television reported Friday that Israeli troops found the body of a fellow soldier in south Lebanon who was killed in clashes the day before in which four other soldiers died.
Lebanese soldiers buried 72 people killed in recent bombings in a mass grave just outside a barracks in the southern city of Tyre. Volunteers put the bodies, many of them children, in wooden coffins and spray-painted the names of the dead on the lids.
The United States -- which has resisted calls to press its ally to halt the fighting -- was sending Secretary of State Condoleezza Rice to the Mideast on Sunday. She ruled out a quick cease-fire as a "false promise" and said "Hezbollah is the source of the problem."
The mission would be the first U.S. diplomatic effort on the ground since the Israeli onslaught against Lebanon began.
Israeli U.N. Ambassador Dan Gillerman said he expected a corridor for food, medicine and other supplies to be opened later Friday or Saturday. His remarks came as French Foreign Minister Philippe Douste-Blazy called for safe passage of urgent aid his country was sending.
U.N. Secretary-General Kofi Annan warned Thursday of a humanitarian crisis in Lebanon and called for an immediate cease-fire, even as he admitted "serious obstacles" stand in the way of easing the violence.
The price of food, medical supplies and gasoline rose as much as 500 percent in parts of Lebanon as the bombardment cut supply routes. The U.N. estimated that a half-million people have been displaced, with 130,000 fleeing to Syria and 45,000 believed to be in need of assistance.
Top Israeli officials said Israel won't stop its offensive until Hezbollah is forced behind the Litani River, 20 miles north of the border -- creating a new buffer zone in a region that saw 18 years of Israeli presence since 1982.
As Israel stepped up its small forays over the border to seek Hezbollah positions, rocket stores and bunkers, it has faced tough resistance.
Israeli warplanes fired missiles that partially collapsed a 1.6-mile suspension bridge linking two steep mountain peaks in central Lebanon. The bridge has been hit several times since fighting began.
The bombing also set ablaze three buses that had just dropped off passengers in Syria, but the drivers escaped, police said.
Renewed attacks struck the ancient city of Baalbek, a major Hezbollah stronghold, and security officials said two people were killed and 19 wounded. Hezbollah strongholds in south Beirut and elsewhere also were struck overnight, killing one person. Missiles hit a village near the Israeli border, Aita al-Shaab, killing three, officials said.
A house in the border village of Aitaroun was flattened, with 10 people believed inside, but rescuers couldn't reach it because of shelling, security officials said.
At least 11 rockets hit Haifa, Israel's third-largest city, and five people were wounded, with 23 treated for shock. More rockets fell elsewhere in northern Israel, the army said, with strikes reported in Rosh Pina, Safed and in several communities near the Sea of Galilee.
Hezbollah has fired hundreds of rockets from the Lebanese border since fighting began, forcing Israelis into underground shelters. Eight people in Haifa were killed July 16.
A U.N. official, speaking on condition of anonymity because of the sensitivity of the situation, said an artillery shell fired by the Israeli military made "a direct hit on the U.N. position overlooking Zarit."
An Israeli military spokesman said the rockets were fired by Hezbollah guerrillas at northern Israel. The differing accounts could not immediately be reconciled.
During an Israeli offensive against Lebanon in 1996, artillery blasted a U.N. base at Qana in southern Lebanon, killing more than 100 civilians taking refuge with the peacekeepers.
The U.N. mission, which has nearly 2,000 military personnel and more than 300 civilians, is to patrol the border line, known as the Blue Line, drawn by the U.N. after Israel withdrew troops from south Lebanon in 2000, ending an 18-year occupation.
Two Apache attack helicopters collided in northern Israel near the border, killing one air force officer and injuring three others, Israeli officials said. Israel's air force began an investigation.
Hezbollah said three of its fighters had been killed in the latest fighting, bringing to six the number killed since Israel began its campaign after the militant Shiite Muslim group captured two of its soldiers July 12.
Annan denounced Israel for "excessive use of force" and Hezbollah for holding "an entire nation hostage" with its rocket attacks and capturing the Israeli soldiers.
The number of reserves called up by the Israeli army was not disclosed, but a military official, speaking on condition of anonymity because of the sensitivity of the information, said it would be several thousand.
Hezbollah leader Sheik Hassan Nasrallah shrugged off concerns of a stepped-up Israeli onslaught, saying the captive Israelis would be freed only as part of a prisoner exchange.
He spoke in an interview taped Thursday with Al-Jazeera to show he had survived an airstrike in south Beirut that Israel said targeted a Hezbollah leadership bunker. The guerrillas said the strike only hit a mosque under construction and no one was hurt.
Lebanese streamed north into Beirut and other regions, crowding into schools, relatives' homes or hotels. Taxi drivers in the south were charging up to $400 per person for rides to Beirut -- more than 40 times the usual price. In remote villages of the south, cut off by strikes, residents made their way out over the mountains by foot.
More than 400,000 people -- perhaps as many as a half-million -- are believed to live south of the Litani, according to former top U.N. adviser Timur Goskel. The river has twice been the border of Israeli buffer zones. In 1978, Israel invaded up to the Litani to drive back Palestinian guerrillas, withdrawing from most of the south months later.
Israel invaded Lebanon again in a much bigger operation in 1982 when its forces seized parts of Beirut. It eventually carved out a buffer zone that stopped at the Litani. That zone was reduced gradually but the Israeli presence lasted until 2000, when it withdrew completely.
Associated Press Writers Edith M. Lederer at the United Nations and Gabe Ross in Haifa, Israel, contributed to this story.