Rocket attacks from Gaza have forced Israelis to flee in ever greater numbers, escalating the belief among Israel's military chiefs that Hamas missiles could threaten the nation's top secret nuclear facility at Dimona.
Israeli officials say that Hamas has acquired dozens of Iranian-made Fajr-3 missiles and with it, an even longer range than previously seen. Many fear that as the group acquires ever more sophisticated weaponry it is only a matter of time before the nuclear installation at Dimona, 20 miles east of Beersheba, falls within its sights.
Dimona houses Israel’s only nuclear reactor and is believed to be where nuclear warheads are stored.
Israeli officials allowed dozens of Palestinian holders of foreign passports to flee the fighting in the Gaza Strip on Friday.
Army spokesman Peter Lerner says nearly 300 Palestinians poured through the Israeli-controlled Erez crossing Friday morning. The Palestinians hold citizenship from a number of other countries, including the U.S., Russia, Turkey and Kazakhstan.
On Thursday an Israeli warplane dropped a 2,000-pound bomb on the home of one of Hamas' top five decision-makers, instantly killing him and 18 others, while the Israeli army said troops massed on the Gaza border were ready for any order to invade.
The airstrike on Nizar Rayan was the first that succeeded in killing a member of Hamas' highest echelon since Israel began its offensive Saturday. The 49-year-old professor of Islamic law was known for personally participating in clashes with Israeli forces and for sending one of his sons on a 2001 suicide mission that killed two Israelis.
The attacks continued Friday. Before dawn, Israeli aircraft hit 15 houses belonging to Hamas militants, Palestinians said. They said the Israelis either warned nearby residents by phone or fired a warning missile to reduce civilian casualties. Twelve people were hurt in the attacks, hospital officials said.
Even as it pursued its bombing campaign, Israel kept the way open for intense efforts by leaders in the Middle East and Europe to arrange a cease-fire. Israel said it would consider a halt to fighting if international monitors were brought in to track compliance with any truce.
Adding to the urgency of the diplomatic maneuvering, the Israeli military said its preparations for a possible ground assault were complete and that troops stood ready to cross the border if the air operation to stamp out Hamas rocket fire needed to be expanded.
Soldiers massed along the Gaza frontier said they were eager to join the fight, and some even cheered as they heard thunderous airstrikes in the distance.
The hit on Rayan's home obliterated the four-story apartment building and peeled off the walls of others around it, creating a field of rubble in the crowded town of Jebaliya in the northern Gaza Strip. Mounds of debris thrown up by the blast swallowed up cars.
Eighteen other people, including all four of Rayan's wives and nine of his 12 children, also were killed, Palestinian health officials said. A man cradled the burned, limp body of a child he pulled from the rubble.
The house was one of five bombed Thursday, among more than 20 targets altogether. Warplanes shredded the houses, taking off walls and roofs and leaving behind eerie, dollhouse-like views into rooms that still contained furniture.
Israel's military, which has said the homes of Hamas leaders are being used to store missiles and other weapons, said the attack on Rayan's house triggered secondary explosions from the arms stockpiled there.
Seven other Palestinians were killed in airstrikes Thursday and one died of earlier injuries.
Israel has targeted Hamas leaders many times in the past, and the current leadership went into hiding at the start of the offensive. Rayan, however, was known for openly defying Israel and in the past had led crowds to the homes of wanted Hamas figures — as if daring Israel to strike and risk the lives of civilians.
Residents said he openly went to a nearby mosque Thursday morning to pray.
In his last interview, recorded with Hamas TV on Wednesday, Rayan was as defiant as ever about confronting the Israeli military.
"Oh fighters, know that you will be victorious," he said. "God promises us either victory or martyrdom. God is greater than they are, God is greater than their planes, God is greater than their rockets."
The military said it had information that there was a tunnel beneath Rayan's home for use as an escape route.
Israel seemed determined to press ahead with airstrikes on Hamas houses. It also has been targeting buildings used by the territory's Hamas government — emptied days ago by evacuations — as well as rocket-launching sites and smuggling tunnels along the border with Egypt.
"We are trying to hit everybody who is a leader of the organization, and today we hit one of their leaders," Israeli Vice Premier Haim Ramon said in a television interview.
More than 400 Gazans had been killed and some 1,700 wounded since Israel embarked on its aerial campaign, Gaza health officials said. The United Nations has said the death toll includes more than 60 civilians, 34 of them children.
One of them, 11-year-old Ismail Hamdan, was buried Thursday after dying of wounds suffered from an airstrike Tuesday that killed two of his sisters, Haya, 4, and Lama, 12. His body was wrapped in a Palestinian flag and his battered face was still bandaged as he was carried above a crowd of mourners.
Since Saturday, three Israeli civilians and one soldier have also died in rocket attacks that have reached deeper into Israel than ever before, bringing more than a tenth of Israel's population of 7 million within rocket range.
The bombing campaign has worsened an already hard life for Gaza's mostly poor population of 1.5 million. On Thursday, hundreds of people stood in long, snaking lines across the territory waiting to buy bread.
Israel launched the offensive Saturday after more than a week of intense Palestinian rocket fire that followed the expiration of a six-month truce, which Hamas refused to extend because Israel kept up its blockade of Gaza.
So far, the campaign has been conducted largely from the air. But a military spokeswoman, Maj. Avital Leibovich, said preparations for a ground operation were complete.
"The infantry, the artillery and other forces are ready. They're around the Gaza Strip, waiting for any calls to go inside," Leibovich said.
Thousands of soldiers waited along the border, resting among tanks, armored personnel carriers and howitzers. The troops watched warplanes and attack helicopters flying into Gaza, cheering each time they heard the explosion of an airstrike.
One soldier, who can be identified under military rules only as Sgt. Yaniv, said he was eager to go in. "I am going crazy here watching all this. I want to do my part as well," he said.
Hamas promised to put up a fight if Israeli land forces invaded.
Hamas is listed as a terrorist organization by the United States and many other Western nations. From 2000 to 2004, Hamas was responsible for killing nearly 400 Israelis and wounding more than 2,000 in 425 attacks, according to the Israeli Ministry of Foreign Affairs.
From 2001 through May 2008, Hamas launched more than 3,000 Qassam rockets and 2,500 mortar attacks against Israeli targets.
"We are waiting for you to enter Gaza to kill you or make you into Schalits," the group said, referring to Israeli Sgt. Gilad Schalit, who was captured in a cross-border raid by Hamas-affiliated militants 2 1/2 years ago and remains in captivity in Gaza.
Israel's bruising campaign has not deterred Hamas from assaulting Israel. According to the military, militants fired more than 30 rockets into southern Israel during the day.
No injuries were reported, but an eight-story apartment building in Ashdod, 23 miles from Gaza, was hit. Panicked residents ran through a debris-strewn street.
Earlier this week, Israeli Prime Minister Ehud Olmert rebuffed a French proposal for a two-day suspension of hostilities to allow for the delivery of humanitarian supplies. Israel has been allowing trucked relief supplies to enter Gaza. Ninety aid trucks crossed the border Thursday.
Still, Olmert seemed to be looking for a diplomatic way out, telling Secretary of State Condoleezza Rice and other world leaders that Israel would accept a truce only if international monitors took responsibility for enforcing it, government officials said. They spoke on condition of anonymity because the talks were confidential.
A Turkish truce proposal included a call for such monitors.
Foreign Minister Tzipi Livni, speaking to reporters during a visit to Paris for meetings with French officials, expressed skepticism about the benefits of a cease-fire. She said Hamas used the lull during the six-month truce that expired last month to build up its arsenal of weapons.
"Our experience from the past is that even when we accept something in order to have a peaceful period of time, they abuse it in order to get stronger and to attack Israel later on," Livni said.
Egypt's foreign minister said Hamas must ensure that rocket fire stops in any truce deal, and he criticized the Palestinian militants for giving Israel an "opportunity on a golden platter" to launch the offensive.
Gaza has been under Hamas rule since the group's fighters overran it in June 2007. The West Bank has remained under the control of moderate Palestinian President Mahmoud Abbas, who has been negotiating peace with Israel for more than a year but has no influence over Hamas. Bringing in truce monitors would require cooperation between the fiercely antagonistic Palestinian factions.
An Abbas confidant said the Palestinian president supported the notion of international involvement. "We are asking for a cease-fire and an international presence to monitor Israel's commitment to it," Nabil Abu Rdeneh said.
World leaders have not been deterred by the initial rejections by Israel and Hamas of truce efforts, and next week French President Nicolas Sarkozy plans a whirlwind trip around the region.
The Associated Press contributed to this report.