Israeli troops surrounded a refugee camp in the Gaza Strip late Thursday - the same area where 11 Palestinians had been killed earlier in the day. The latest raid follows rocket attacks from Gaza at communities inside Israel.
Palestinian witnesses say about 100 Israeli tanks and armored vehicles were seen moving towards the Jabalya refugee camp.
The action comes less than a day after a previous nine-hour raid in the camp, during which 11 Palestinians were killed.
The Israeli army launched its latest operation, following the firing of home-made Kassam rockets from Gaza at the nearby Israeli town of Sderot.
No injuries or damage were reported to have been caused by the rockets, the third of which appears to have been fired from the Jabalya camp.
Israeli army spokeswoman Sharon Feingold says major efforts are being made in Gaza to halt such attacks, which have become more frequent in recent weeks.
"Our need to be there [in the Gaza Strip] is to try and prevent this launching of Kassam rockets which is basically a terrorist activity, shooting at communities, shooting at Israeli towns is a terrorist action and if we are not there then it is much easier for them to carry out this terrorist activity," he said.
Hamas, the Islamic Resistance Movement, took responsibility for the firing of the Kassam rockets, Israel Radio reported.
The Israeli army has launched a major crackdown against Hamas, after the organization planted a bomb in the Gaza Strip last month that destroyed an Israeli tank and killed four soldiers.
Israel also believes that Hamas was behind the suicide bombing on a bus in Haifa on Wednesday, which killed at least 15 people and left scores more wounded.