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Smoke rises during an explosion from an Israeli forces strike in Gaza City, Saturday, Nov. 17, 2012. Israel bombarded the Hamas-ruled Gaza Strip with nearly 200 airstrikes early Saturday, the military said, widening a blistering assault on Gaza rocket operations by militants to include the prime minister's headquarters, a police compound and a vast network of smuggling tunnels.
ABOARD AIR FORCE ONE—The White House on Saturday defended Israel's right to defend itself against attack and decide how to respond to rocket fire from the Gaza Strip, blaming the ruling Islamic militant Hamas group for starting the conflict.

Obama and Israeli Prime Minister Benjamin Netanyahu are in agreement that a de-escalation of the violence is preferred, provided that Hamas stops sending rocket into Israel, deputy national security adviser Ben Rhodes told reporters during the president's flight on Air Force One to Asia.

Israel launched the offensive on Wednesday by assassinating Hamas' military commander, but Rhodes said the U.S. believes "the precipitating factor for the conflict was the rocket fire coming out of Gaza. We believe Israel has a right to defend itself, and they'll make their own decisions about the tactics they use in that regard."

He added, "These rockets have been fired into Israeli civilian areas and territory for some time now. So Israelis have endured far too much of a threat from these rockets for far too long, and that is what led the Israelis to take the action that they did in Gaza."

The Israeli government has called up thousands of reservists and massed troops, tanks and other armored vehicles along the border with Gaza, signaling a ground invasion could be imminent.

Obama has spoken with President Mohammed Morsi of Egypt and Prime Minister Recep Tayyip Erdogan of Turkey about the situation.

"They have the ability to play a constructive role in engaging Hamas and encouraging a process of de-escalation," Rhodes said.

Israel on Saturday hit Gaza with nearly 200 airstrikes, expanding an aerial assault to include the prime minister's headquarters, a police compound and a vast network of smuggling tunnels.

"We wouldn't comment on specific targeting choices by the Israelis other than to say that we of course always underscore the importance of avoiding civilian casualties," Rhodes said. "But the Israelis again will make judgments about their military operations."

Forty-two Palestinians, including 13 civilians, and three Israelis have been killed in this past week's fighting.