Israel’s retaliatory airstrikes on Iran this weekend caused “significant damage,” despite US President Joe Biden urging restraint and vetoing numerous potential targets, a security expert said.

Farzin Nadimi, a security analyst and a senior fellow at the Washington Institute, told Iran International that Israel’s four-hour bombardment achieved a "very significant result”, in spite of Washington urging the Jewish state to moderate its response to nearly 200 ballistic missiles fired at Israel this month.

Sites including a former nuclear testing site closed down in 2003 and military facilities were hit in the barrage.

He said the attack should not be overestimated, however. "Had Israel intended to target Iran's air defense, including its command-and-control centers, it would have to carry out a more complex, prolonged, and riskier operation."

According to Nadimi, some of those more risky targets are located "under mountains and underground," adding that attacking them is not possible solely with air-launched ballistic missiles.

Reuters reported that the attack came after weeks of the Biden administration tempering the nature of Israel’s response to an attack which many feared would see a regional war erupt.

Fearing a major flare-up between the longtime foes, the US President, Joe Biden, and the administration, have been in regular contact with Israeli officials to keep the retaliation “proportional”.

A senior US official told Iran International that the US “does not approve targets, nor do we want to take that responsibility”, however, as the region sits on the edge of an all-out war, Washington has been critical in tempering Israel’s response.

Reuters reported that just hours after Iran’s massive missile barrage, the administration sent an urgent message to Israel urging them to take a breath, and make a calculated response to the two consecutive attacks which sent the entire nation into bomb shelters.

Citing current and former US officials, Reuters reported that the US had done its utmost to influence the nature of the response, making clear it would not support strikes on Iran’s nuclear facilities.

While Israel destroyed key Iranian air defenses and missile production facilities, weakening Iran's military, the attack avoided Iran's sensitive nuclear sites and energy infrastructure, meeting Biden's two top demands.

"US pressure was critically important," said Jonathan Panikoff, a former deputy U.S. national intelligence officer for the Middle East, speaking to Reuters.

"Israeli decision-making would have been far different had the Biden administration not taken measures to push Israel not to strike nuclear or energy sites,” he added.

The Israeli strikes, in addition to targeting air defense sites, hit missile production facilities across Iran.

Commercially available satellite imagery revealed significant damage at the Parchin military complex, one the most expansive and secretive Iranian missile production facilities.

Some of the targets at the missile facilities were sophisticated mixing machines used to make solid fuel for advanced ballistic missiles, such as those that Tehran has used to attack Israel directly.

The Institute for the Study of War assessed that “Iran will likely need months or possibly a year or more to acquire new mixing equipment.”

“The Israel Defense Forces (IDF) inflicted serious damage to the Iranian integrated air defense network during its strikes on Iran on October 25,” its analysis said.

Israeli Prime Minister Benjamin Netanyahu has denied that Israel avoided striking Iranian gas and oil facilities because of US pressure.

"Israel chose in advance the attack targets according to its national interests and not according to American dictates," he said.

President Biden was quick to say that the US supported Israel’s right to defend itself and make clear he supported a “proportionate” retaliation, but made clear he would not stand behind a global war triggering attack on Iran’s nuclear sites.

"In the hours after that attack, we promised serious consequences for Iran," according to one senior Biden administration official speaking to Reuters.

US Defense Secretary Lloyd Austin held around a dozen calls with his Israeli counterpart, Yoav Gallant, since this month’s attack, the two having a strong relationship which has been key since the outbreak of the Gaza war, triggered by Iran-backed Hamas.

"We knew they were getting ready to do something, and he was pushing for it to be proportional," one US official told Reuters of Austin's conversations with Gallant.

The US Secretary of State Antony Blinken was a key player in shoring up global support for Israel’s right to defend itself, with both Western and Arab allies alike, explaining that Israel would have to respond but assuring them that Washington was working to calibrate it.

Iran’s second barrage this year was also significant. Jeffrey Lewis, a non-proliferation expert at the Middlebury Institute of International Studies, said that analysis of satellite imagery showed at least 30 impacts at Israel's Nevatim Airbase alone.

It has raised questions as to whether Israel was trying to conserve dwindling air defenses or simply thought that the hardened facility would be less expensive to repair than to repel each projectile fired by Iran, Lewis told Reuters.

"Israel may have decided that the stockpiles were running low or that interceptors were just too expensive to use on ballistic missiles," Lewis said.

One US official told Reuters that Iran’s nuclear and oil sites were on the list of potential targets, but to counter this, Washington worked to impose oil sanctions targeting Iran's so-called "Ghost Fleet" to offer an alternative measure to the Israelis who wanted to damage Iran's oil revenues with a kinetic strike.

The United States had worked to bolster Israel's air defenses ahead of its Saturday strike on Iran including a rare US deployment of the Terminal High Altitude Area Defense system, or THAAD, to Israel along with about 100 US soldiers to operate it.

But it came on the condition of knowing the plans beforehand, according to Reuters, hashed out in a call between Israeli Prime Minister Benjamin Netanyahu and Biden on October 9, in which a general plan was shared.

The US also shored up support from Europe which levied more sanctions on Iran Air, and showing the world that US had Israel's back were other key elements of this "package" of alternative measures, while trying to avert an all-out war.

Since the October ballistic missile bombardment, the US military also carried out a strike against the Iran-aligned Houthis in Yemen with long-range B-2 stealth bombers, another message to show it was working against Tehran.

As the threat of an Iranian response looms large, US support continues, with Israel playing ball with its most powerful and needed ally. ”If Iran chooses to respond once again, we will be ready, and there will be consequences for Iran once again. However, we do not want to see that happen," the senior Biden administration official told Reuters.

Mike Turner, a Republican congressman who chairs the House Intelligence Committee recently told Fox News, "They've limited the ability for Israel to really impact Iran and its ability to continue to threaten Israel."

Aaron David Miller, a senior fellow at the Carnegie Endowment for International Peace, said the approach may not be the same should Donald Trump win the upcoming elections.

"If Trump wins this election, I think that the Israelis will perhaps even look for opportunities in the months ahead, now that they've demonstrated that they can get away with dismantling Iran's air defense systems and essentially doing a good deal of damage," Miller said.

Since October 7 last year, when Hamas, designated a terror group in countries including the US and UK, attacked Israel, Iran’s militias around the region have risen up in support of the Gaza-based militia.

Israel has endured attacks from Yemen’s Houthis, Lebanon’s Hezbollah, and militias in Iraq, the West Bank, and Syria, in addition to direct attacks from Tehran.