By Martin Patience
BBC News, Jerusalem
Israel has vowed to stop rocket attacks by Palestinian militants from Gaza on Israeli communities lying close to the territory. The military moved into areas of northern Gaza used by militants to fire the rockets - effectively creating a security buffer zone.
Initially the Israeli military said it launched the incursion into Gaza to try to pressure Palestinian militants to release the captured Israeli soldier, Cpl Gilad Shalit.
Israeli military officials say it will not be a permanent presence
But after Palestinian militants continued firing Qassams - crude home-made rockets - from Gaza into Israel, the operation's objective was widened to prevent the rocket fire.
Officials say there are no plans to reoccupy Gaza or carve out
a permanent buffer.
"We have no intention of drowning in the Gaza swamp," Defence Minister Amir Peretz said on Wednesday.
But some Israeli security analysts are warning that is just what the army risks - getting sucked into the "swamp".
"It's easy to go in, but difficult to pull out," says Yossi Alpher, the former director of the Jaffee Centre for Strategic Studies at Tel Aviv University.
Easy to fire
When a Qassam hit the major Israeli city of Ashkelon for the first time, Israel's security cabinet instructed the army to prepare for a long battle focusing on "institutions and infrastructure facilitating terrorism".
What this will involve is not clear as the Israeli army has refused to give specific details on the operation.
But the Israeli daily newspaper Haaretz reported that the army wanted to capture a broad swathe of territory about one-and-a-quarter kilometres into Northern Gaza to prevent rockets being fired.
Clashes have worsened since the military action began
Some Israeli security analysts, however, warn that it will be impossible to prevent all the rocket launches.
"I don't think you can stop them firing Qassams 100%," says Yossi Alpher. "They are very easy to travel with and easy to fire."
Drawing on Israel's experience in Lebanon, where the army got entangled in a bloody, decades-long occupation, Mr Alpher says the Israeli military could get drawn further into Gaza than it wants.
The rocket attacks on Ashkelon suggest that Palestinian militants have developed Qassams with a greater range, meaning that they could still hit Israeli communities even if they were not fired from northern Gaza.
"It's a slippery slope: You begin in the north and end up in the south of Gaza," he says.
Jonathan Fighel, a senior researcher at the International Policy Institute for Counter-Terrorism, says that Israel needs to develop a strategy that will prevent itself from getting bogged down in northern Gaza.
"The buffer zone needs to be flexible," he says. "There can't be Israeli troops located in it every day. The troops need to be mobile otherwise they become a target.
"Israel needs to create the notion that while there are not troops in the buffer zone 24 hours a day, Palestinians think that there are."
But Mr Fighel says the best solution would be negotiations to settle the conflict between Palestinians and Israelis. "There really is no substitute," he says.