"We are in control of the communities," military spokesman Daniel Hagari said. However, there still might be "terrorists" in the area, he said.

This comes after Israel said that it has brought in special forces to try to wrest control of four sites from Hamas after Tel Aviv formally declared war and gave the green light for “significant military steps” to retaliate. More than 1,100 people have been killed and thousands wounded on both sides. Fighting continued in several locations.

Israel's chief military spokesman said troops had re-established control of communities that had been overrun while isolated clashes continued.

"We are now carrying out searches in all of the communities and clearing the area," chief military spokesperson Rear-Admiral Daniel Hagari said.

Earlier, another spokesman, lieutenant colonet Richard Hecht, acknowledged that it was "taking more time than we expected to get things back into a defensive, security posture".

Israel has responded with its heaviest ever bombardment of the Gaza Strip, killing some 500 people so far.

Meanwhile, Hamas spokesman Abdel-Latif al-Qanoua told The Associated Press that the group's fighters continued to battle outside Gaza and had captured more Israelis. The group aims to free all Palestinian prisoners held by Israel, he said.