The current bombing campaign, which the Israel Defense Forces has dubbed Operation Protective Edge, has used 400 tons of explosives against targets in Gaza, the Jerusalem Post quoted an anonymous senior Israeli security source as saying.

“Hamas has been surprised by Israel’s response. We systematically struck operational infrastructure, where Hamas commanders operate,” the source said, according to the Post. “There’s not a single Hamas brigade commander that has a home to go back to.”

Meanwhile, some 72 rockets fired from Gaza struck Israel on Wednesday, the second day since the launch of the IDF campaign in Gaza. Three of the rockets were fired at Dimona, the site of Israel’s nuclear plant; one was intercepted by the Iron Dome missile defense system and the other two fell in open areas.

The farthest-reaching rocket so far landed in the vicinity of Zichron Yakov, an Israeli town situated about 80 miles north of Gaza, just south of Haifa. Haifa, which came under heavy rocket fire from the north during Israel’s 2006 war with Hezbollah in Lebanon, announced Wednesday that it was reopening its bomb shelters.

Gaza rocket crews also have targeted Jerusalem, Tel Aviv and Israel’s airport, where incoming flights have changed their usual landing routes as a safety precaution. El Al, Israel’s national airline, announced Wednesday that it would allow travelers with bookings to Israel through July 18 to cancel or reschedule their trips at no extra charge.

Though Israel’s Cabinet authorized the call-up on Tuesday of up to 40,000 reserve troops, the IDF has yet to mobilize significant numbers of reservists.

Israeli Prime Minister Benjamin Netanyahu warned that Palestinian terrorists would pay a “heavy price” for their rocket fire against Israel and said he is prepared to “further intensify attacks on Hamas.” President Shimon Peres said an Israeli ground offensive could happen in Gaza “quite soon.”

Palestinian Authority President Mahmoud Abbas said that the IDF’s “killing of entire families is genocide by Israel against our Palestinian people,” Agence France-Presse reported.

So far, about 40 Palestinians in Gaza have been reported killed in the operation. Israel has not reported any deaths.

The hostilities between Israel and Gaza come in the wake of the murder of three Israeli teenagers abducted last month from a hitchhiking post in the West Bank, and the subsequent murder by Jewish extremists of a Palestinian teenager in Jerusalem. The murder of the Palestinian was followed by Palestinian rioting and rocket fire from Gaza.

Israel has arrested six suspects in the case of the murdered Palestinian teen. Suspects in the murder of the Israeli teens have yet to be apprehended but they are presumed to be Palestinian.