By Trevor Hunnicutt, Matt Spetalnick and Jasper Ward
WASHINGTON (Reuters) -U.S. President Joe Biden said on Wednesday he would not support any Israeli strike on Iran's nuclear sites in response to its ballistic missile attack and urged Israel to act "proportionally" against its regional arch-foe.
Biden spoke a day after Iran fired more than 180 missiles at Israel, an operation he previously described as "ineffective." Israeli Prime Minister Benjamin Netanyahu vowed Iran would pay for the attack.
"We'll be discussing with the Israelis what they're going to do, but all seven of us (G7 nations) agree that they have a right to respond but they should respond proportionally," Biden told reporters before boarding Air Force One.
Some analysts said Israel's response would likely be sharper than when Iran launched missiles and drones at Israel in April, suggesting this time it could target Tehran's nuclear or oil facilities. Other experts expected the U.S. to try again to moderate Israel's response in an effort to avoid a regional war.
Asked whether he would back Israel striking Iranian nuclear sites as it has long threatened, Biden told reporters: "The answer is no."
Biden said more sanctions would be imposed on Iran and he would speak soon with Netanyahu.
"Obviously, Iran is way off course," he said.
Israeli officials have told U.S. counterparts they are still finalizing targets, timing and means for a response to Iran's missile attack, according to a person in Washington familiar with the discussions.
Israel may not feel compelled to strike back immediately, given its success in thwarting the Iranian attack. But it is unlikely to wait for long out of concern a retaliatory move would lose effectiveness as a deterrent if delayed, the U.S. source said.
Unlike in the aftermath of the Iran’s April attack, the U.S. is not pressing Israel to refrain from retaliation but wants Israel to carefully consider potential consequences first, the source said.
Iran's missile attack escalated tensions in the region, where the Biden administration has for months led intense negotiations on a ceasefire in the nearly year-old Israel-Hamas war in Gaza and regularly predicted one was imminent.
Biden, in the waning months of his term, already faces sharp criticism at home and abroad for staunch U.S. military support of Israel, as does his vice president and the Democrats' presidential candidate, Kamala Harris.
'KNIFE'S EDGE'
At a virtual event hosted by Washington-based think tank Carnegie Endowment on Wednesday, U.S. Deputy Secretary of State Kurt Campbell repeated the U.S. view that Tehran's move was "deeply irresponsible" and there must be a "return message."
But with the Middle East on a "knife's edge," the U.S. is concerned about "an even broader escalation" that could imperil both Israeli and U.S. strategic interests, he said.
"I think we tried to underscore our support for some of the actions that Israel has taken," he added. "We have real wariness about a extended or substantial ground set of operations in Lebanon."
Netanyahu has not always heeded the Biden administration's advice in the current Middle East conflict.
The Israeli army is locked in combat at its northern border with Lebanon's Iran-backed Hezbollah fighters. On Wednesday, eight Israeli soldiers were killed -- the deadliest day for Israel's military on the Lebanon front in the past year of border-area clashes between Israel and Hezbollah.
Iran said on Wednesday its missile volley - its biggest ever assault on Israel - was over, barring further provocation.
Israel has long considered Iran's nuclear program an existential threat, though Tehran has insisted it is not seeking a nuclear weapon. Iran's nuclear facilities are spread over many locations, some of them deep underground.
Iran agreed to restrictions on its nuclear activities under a U.S.-led international deal in 2015. That pact fell apart after then-President Donald Trump pulled the U.S. out in 2018.
Iran has been expanding its uranium enrichment program ever since, reducing the so-called "breakout time" it would need to produce enough weapons-grade uranium for a nuclear bomb to a matter of weeks from at least a year under the 2015 accord.
(Reporting by Trevor Hunnicutt, Jasper Ward and Matt Spetalnick; additional reporting by by David Brunnstrom, Humeyra Pamuk, Simon Lewis, Daphne Psaledakis and Michael Martina; writing by Matt Spetalnick; Editing by Caitlin Webber, Jon Oatis and Cynthia Osterman)
