Israeli airstrikes over the Gaza Strip peaked Thursday night, with dozens of dugouts used by Palestinian militants for firing rockets struck by fighter jets and helicopter gunships within the course of an hour, Israeli army said.

"Approximately 70 underground sites for launching medium-range rockets were targeted in a rapid and coordinated strike, and direct hits were confirmed," a military spokesman told Xinhua.

He said the sites that have been targeted were "positively identified" via precise intelligence collected over months, and that the operation aimed to "significantly impair" the rocket- launching capabilities of militant groups.

The aerial assault came shortly after Hamas extended rocket fire to central Israel. Two projectiles landed near Tel Aviv, early in the evening. One reportedly landed south of the municipal line and the other in the water off the shore of the suburb of Bat Yam. Earlier, rockets had exploded in open areas near Rishon Letzion, some 20 km south of Tel Aviv.

The intense rocket fire, which early Thursday claimed the lives of three civilians, and with more than 270 projectiles fired at southern Israel in the past 30 hours, has raised speculation that a ground offensive is in the offing.

The Israeli Defense Ministry on Thursday evening announced that it has requested government approval to mobilize 30,000 reservists, while Defense Minister Ehud Barak and the army's top brass convened in Tel Aviv to deliberate further military action in the coastal territory.

Meanwhile, large forces, including tank brigades and infantry units, are already deployed along the border ahead of a possible ground operation.

Israeli airstrikes have so far hit more than 200 targets in Gaza, killing some 19 Palestinians and injuring more than 145 others, according to the Palestinian Health Ministry.