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Associated Press
In this Jan. 20, 2012 file photo, Israeli Chief of Staff Lt. Gen. Benny Gantz, right, gestures as he stands with U.S. Army Gen. Martin Dempsey, Chairman of the Joint Chiefs of Staff, during a welcoming ceremony in a military base in Tel Aviv, Israel.

JERUSALEM — Officials are quietly conceding that new international sanctions targeting Iran's suspect nuclear program, while welcome, are further constraining Israel's ability to take military action — just as a window of opportunity is closing because Tehran is moving more of its installations underground.

The officials say that Israel must act by the summer if it wants to effectively attack Iran's program.

A key question in the debate is how much damage Israel, or anyone else, can inflict, and whether it would be worth the risk of a possible counterstrike.

Israel has been a leading voice in the international calls to curb Iran's nuclear program. Like the West, it believes the Iranians are moving toward nuclear weapons capability — a charge Tehran denies.

Israel contends a nuclear-armed Iran would threaten its survival, citing Tehran's calls for the destruction of the Jewish state and its support for anti-Israel militant groups. It also fears an Iranian bomb would touch off a nuclear arms race in a region still largely hostile to Israel.

Israel refuses to rule out the use of force, saying that "all options are on the table."

In comments Friday to the World Economic Forum in Davos, Switzerland, Israeli Defense Minister Ehud Barak said time was running out for the world to act.

"We are determined to prevent Iran from turning nuclear," he said. "It seems to us to be urgent, because the Iranians are deliberately drifting into what we call an immunity zone where practically no surgical operation could block them."