Palestinian security sources said 35 tanks were seen entering Bait Hanun, while another 30 were seen pushing into Bait Lahya and 30 more were spotted moving into the eastern sector of Jabalya early on Friday.
The Israeli military offensive - named Operation: Days of Penitence - would see Israeli troops deploy in parts of the Jabalya refugee camp as well as Bait Hanun in a bid to stop Palestinian fighters firing homemade rockets into Israel, Israeli army radio said.
The radio described the operation as allegedly intended to set up a buffer zone to keep Palestinian rockets out of range of Israeli towns, such as one that killed two children in the town of Sderot on Wednesday.
Israeli officials indicated the operation might last for several weeks but would be limited to the northern Gaza Strip.
Civilians paying price
On a day that has seen Israeli soldiers kill 32 Palestinians and wound more than 102 during their incursion into northern Gaza, Sharon's approval is believed to cater to Israeli military leaders who have called for "aggressive and ongoing activity" against Palestinian fighters.
The latest Israeli attack is the
bloodiest since 2002
The toll on Thursday marked the bloodiest day in two years in the coastal strip. Three Israelis were also killed in attacks in Gaza.
In an exclusive interview with Aljazeera.net, Colonel Yoav Mordechai of the Israeli District Civil Liaison Office said there is no time limit to Israeli operations seeking to weed out Qassam rockets in Gaza.
"If there are rockets being fired from a certain area, we will go into it. We have no intention to occupy the Gaza Strip," he said.
He also denied reports that five Israeli tanks had been destroyed during military operations in occupied Gaza.
Rocket attacks increase
Despite intrusive incursions into heavily-populated civilian areas of Gaza to seek and destroy Qassam launches in the past several months, Palestinian fighters have been able to evade Israeli operations and have intensified their rocket attacks.
"From a tactical point of view, we are studying this. The problem is the terrorists are firing from areas where civilians are located, from schools and houses, they are firing RPGs (rocket-propelled grenades) against our tanks," Mordechai said.
When asked why Israeli gunners do not use their technological advantage to minimise civilian deaths, Mordechai said: "The terrorists are using Gazans as human shields and the civilians are paying the price for this."
Gaza correspondent Laila El-Haddad contributed to this report