CBS News correspondent Robert Berger reports that Israeli tanks and troops are crossing the border, and that there are are approximately 10,000 Israeli soldiers deployed on the Gaza frontier, including elite infantry units, the engineering corps and special forces.
Israeli television is reporting that the army has been operating on the ground in Gaza "for the past hour." Channel 10 also reports the army is operating in a "limited area" in Gaza.
Berger says that Israeli forces plan to seize control of Hamas rocket launching sites, which is a risky move — Hamas has dug in to bunkers and tunnels, and is well-armed.
Artillery units had joined Israeli bombardment on Gaza for the first time. Heavy artillery fire in the early evening was intended to detonate Hamas explosive devices and mines planted along the border area before troops marched in.
It was the latest turn of events as Israel's offensive entered its second week.
Warplanes and gunboats blasted more than two dozen Hamas positions earlier on Saturday, targeting weapons storage facilities, training centers and homes of leaders.
There were tentative signs that the current phase of aerial attacks was nearing its end; most of the airstrikes targeted empty buildings and abandoned sites, suggesting the Israeli air force may be running out of targets.
One airstrike today, on a mosque in the northern town of Beit Lahiya, killed 13 people and wounded 33 others, several in critical condition.
It is not clear whether the dead were Hamas militants. The mosque is named after a founder of the militant group who was killed by Israel in 2004.
More than 440 Palestinians have been killed in the past week and the U.N. says that 2,000 have been wounded, "a significant number of them" women and children.
Four Israelis have also been killed, and rocket attacks on southern Israel persist.
Palestinian militants fired at least 10 rockets into southern Israel, lightly wounding one person, police said. One rocket scored a direct hit on a house in the southern city of Ashkelon and another struck a bomb shelter there, leaving its aboveground entrance scarred by shrapnel.
This latest round of violence erupted after the expiration of a six-month cease-fire that was repeatedly marred by sporadic rocket attacks on Israel.
In the latest attacks on Gaza, the army struck the homes of two Hamas operatives, saying the buildings were used to store weapons and plan attacks. Hamas outposts, training camps and rocket launching sites also were targeted, it said.
It also struck the American International School, the most prestigious educational institution in Gaza. The school is not connected to the U.S. government, but teaches an American curriculum in English.
Israel claimed the school was being used to store rockets, reports CBS News correspondent Sheila MacVicar.
The airstrike demolished the school's main building and killed a night watchman.
Two other Palestinians were killed in a separate airstrike, while four others, including a midlevel militant commander, died of wounds sustained earlier, Gaza health officials said.
Early Saturday, the army preceded airstrikes with a drop of leaflets in downtown Gaza City asking people to evacuate.
But, MacVicar notes, most have absolutely no place to go … and there is no place anyone could be sure to be safe.
A lucky few are escaping, foreign-born wives and children of Palestinian men. And they are leaving their husbands and fathers behind to who-knows-what fate.
Israel briefly opened its border Friday to allow nearly 300 Palestinians with foreign passports - foreign-born wives and children of Palestinian men - to flee the besieged area. The evacuees told of crippling shortages of water, electricity and medicine.
Robert Serry, U.N. Special Coordinator for the Middle East Peace Process, said, "Protection of civilians, the fabric of Gaza, the future of the peace process and regional stability all are trapped between the irresponsibility of Hamas rocket attacks and the excessiveness of Israel's response.
"And as you know, with Israeli tanks on Gaza's border, it is absolutely imperative now that we find an immediate and lasting way out to avoid an even deeper and deadlier conflict," Serry said.
Israel insists it will continue to prosecute this conflict until there is no more rocket fire, MacVicar said. Hamas militants did launch more longer range missiles this morning; they caused no casualties.
Israel's airstrikes have badly damaged Gaza's infrastructure, knocking out power and water in many areas and raising concerns of a looming humanitarian disaster.
"There is a critical emergency right now in the Gaza Strip," said Maxwell Gaylard, U.N. humanitarian coordinator for the Palestinians Territories.
Israel denies there is a humanitarian crisis in Gaza and has increased its shipments of goods into Gaza. It says it has confined its attacks to militants while trying to prevent civilian casualties.
"Good Will Alone Isn't Going To Disarm Hamas"
While President Bush blamed Hamas for the conflict, a Hamas supporter criticized what he called the international community's "double standard" when it came to the aggression in Gaza.
While President-elect Barack Obama appears well-prepared as he transitions to the Oval Office, Michael O'Hanlon, senior fellow at the Brookings Institution, said on CBS' The Early Show that "no one is properly prepared for handling a Middle East crisis.
"Look at the basic choice as it's shaping up," O'Hanlon told Early Show anchor Erica Hill. "One is try to have some kind of a 'verifiable' ceasefire. Fourteen-thousand U.S. troops in Lebanon have not been able to prevent Hezbollah from rearming after the 2006 summer war. Fourteen-thousand people couldn't do it there. I don't know what kind of truly rigorous ceasefire arrangement could be worked out.
"What is the alternative? Israel going on the ground and perhaps overthrowing Hamas and waiting for the world to figure out what should replace it."
But replacing Hamas with another ruling authority may be a diplomatic quagmire. "In the short term no one wants to work with Israel to replace Hamas, and if you did as a Palestinian you would be discredited and someone working with the enemy. The world has to figure out an interim group or U.N. trusteeship to administer that territory."
O'Hanlon said that Obama's pick for Secretary of State, Sen. Hillary Clinton, has an advantage over Condoleezza Rice: an association to a former president, Bill Clinton, who is regarded in a fairly positive light. "Not to mention the Obama aura, because so much hope is surrounding his incoming presidency," he said. "On the other hand, you have to figure out some way to disarm Hamas, and good will is not going to do that by itself."
For that reason O'Hanlon is positive about Obama's incoming national security advisor, Gen. Jim Jones. "He has been working on reform of the Palestinian security sector in his recent past. I think that may be the crux of the matter and the key to getting out of this. If we can figure out some international supervision for reform of the Palestinian security forces. But, again, that presupposes figuring out what to do with Hamas."
Increasing International Pressure For A Ceasefire
MacVicar reports that, with the equivalent of a green light from President Bush (who in his Saturday address blamed Hamas rocket attacks for the recent conflict), Israel continues to make preparations for what seems increasingly inevitable - a ground invasion of Gaza.
Israeli defense officials said some 10,000 troops, including tank, artillery and special operations units, were prepared to invade. The officials said top commanders are split over whether to send in ground forces, in part because such an operation could lead to heavy casualties as well as a belief that Hamas already has been dealt a heavy blow. The officials spoke on condition of anonymity because they were discussing classified discussions.
Exiled Hamas leader Khaled Mashaal, speaking from Damascus, Syria, warned that any ground assault would lead Israel to "a black destiny of dead and wounded." He asserted that the group had sustained minimal losses.
He did, however, say Hamas was "ready to cooperate with any effort leading to an end to the Israeli offensive against Gaza, lifting the siege and opening all crossings."
The international push for a truce could play a big role in whether Israel invades. French President Nicolas Sarkozy is visiting the region next week, and U.S. President George W. Bush and U.N. chief Ban Ki-moon both spoke in favor of an internationally monitored truce.
Israel has already said it is open to the idea of international monitors. It is unclear whether Hamas would agree to such supervision, which could limit its control of Gaza. Hamas has ruled the area since seizing control in June 2007.
In Hamas' first reaction to the proposal for international monitors, government spokesman Taher Nunu said the group would not allow Israel or the international community to impose any arrangement, though he left the door open to a negotiated solution. "Anyone who thinks that the change in the Palestinian arena can be achieved through jet fighters' bombs and tanks and without dialogue is mistaken," he said.
Israel's call for international monitors appeared to be gaining steam.
At the United Nations, Ban urged world leaders to intensify efforts to achieve an immediate cease-fire that includes monitors to enforce the truce and possibly protect Palestinian civilians.
In Washington, Mr. Bush branded the rocket fire an "act of terror" and outlined his own condition for a ceasefire in Gaza, saying no peace deal would be acceptable without monitoring to halt the flow of smuggled weapons to terrorist groups.
"The United States is leading diplomatic efforts to achieve a meaningful ceasefire that is fully respected," Bush said in his weekly radio address. "Another one-way ceasefire that leads to rocket attacks on Israel is not acceptable. And promises from Hamas will not suffice."
Secretary of State Condoleezza Rice continued furious telephone diplomacy to arrange a truce, but said she had no plans to make an emergency visit to the region.
Palestinian President Mahmoud Abbas delayed a planned trip to the United Nations so he could meet with Sarkozy and a high-level EU delegation on Monday. He now plans on speaking at the U.N. on Tuesday, said Abbas aide Saeb Erekat.
At the U.N., Abbas is expected to urge the Security Council to adopt an Arab draft resolution that would condemn Israel and demand a halt to its bombing campaign in Gaza.
Abbas, whose forces in Gaza were ousted by Hamas in June 2007, still claims authority over the area.
The council is expected to discuss the draft resolution on Monday. But the United States said the draft is "unacceptable" and "unbalanced" because it makes no mention of halting the Hamas rocket attacks.