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.

Israeli leaders say they prefer a diplomatic solution. But – skeptical of international resolve – Israel refuses to rule out the use of force, saying frequently that “all options are on the table.”

In comments Friday to the World Economic Forum in Davos, Switzerland, Israeli Defense Minister Ehud Barak called for even tougher sanctions against Iran and 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.”

Returning Monday to Israel, Barak added: “We must not waste time on this matter; the Iranians continue to advance (toward nuclear weapons), identifying every crack and squeezing through. Time is urgently running out.”

Key Israeli defense officials believe that the time to strike, if such a decision is made, would have to be by the middle of this year.

Complicating the task is the assessment that Iran is stepping up efforts to move its work on enriching uranium – a critical component of bomb-making – deep underground.

A team of U.N. nuclear inspectors, including senior weapons experts, is in Iran this week, and the findings from the visit could greatly influence Western efforts to expand economic pressures on Tehran over its uranium enrichment.

The European Union this month decided to stop importing oil from Iran – just weeks after the U.S. approved, but has yet to enact, new sanctions targeting Iran’s Central Bank and, by extension, its ability to sell its oil.

An Israeli strike would risk shattering the U.S.-led diplomatic front that has imposed four additional rounds of sanctions on Iran and jolt the shaky world economy by causing oil prices to spike. Still, officials say, if Israel feels no alternative but to take military action, it will do so.

Israel possesses dozens of F-16s and F-15s, some customized with long-range fuel tanks, and has bought additional Dolphin submarines from Germany capable of firing nuclear missiles.

It introduced a fleet of huge pilotless planes known as Heron TPs that can reach the Persian Gulf, provide surveillance and be used for aerial refueling – likely a critical aspect of any Iran mission. One of the Herons, which are the size of Boeing 737s, crashed during a test flight Sunday.

The U.S. has sold Israel dozens of 100 GBU-28 laser-guided “bunker-buster” bombs. The 2.5-ton bombs are capable of penetrating more than 20 feet (6 meters) of solid concrete.