Iran fired nearly 200 ballistic missiles at Israel, Tehran's largest-ever direct attack on its archenemy.
The October 1 attack was bigger and bolder than Iran's unprecedented strikes on Israel in April. Tehran also used more advanced missiles and gave little warning before launching its latest attack.
The full extent of the damage and casualties caused by Iran's missile attack is still unclear. But Israel has vowed a severe response.
Experts said Israel's retaliation is likely to be stronger compared to April, when its response was relatively muted, given the larger scale of Iran's latest direct attack.
"Israel is certainly going to deal a much more devastating blow to Iran," said Ali Vaez, director of the Iran Project at the International Crisis Group.
Israel Counts The Cost After Iranian Missile Barrage
Risking Israeli Retaliation
Iran described its October 1 attack as retaliation for Israel's invasion of Lebanon and devastating yearlong war in the Gaza Strip as well as Israel's recent assassinations of key Iranian allies in the region.
Israeli forces launched a ground invasion of southern Lebanon on October 1 following a week of devastating air raids.
Israeli air strikes in Beirut on September 27 killed Hassan Nasrallah, the leader of Hezbollah, the Iran-backed armed group and political party that controls much of southern Lebanon.
Israeli attacks have decimated the leadership and degraded the fighting capabilities of Hezbollah, Iran's closest ally and key to Tehran's strategy of deterrence against Israel. Hezbollah is a U.S.-designated terrorist organization, although the EU has only blacklisted its armed wing.
Meanwhile, Ismail Haniyeh, the political head of the U.S.- and EU-designated Palestinian terrorist group Hamas and an ally of Iran, was killed in a suspected Israeli attack in Tehran in July.
Experts said domestic pressure to respond to Israel and Iran's weakening position in the region forced Tehran's hand.
"Iran seems to have come to the conclusion that the costs of inaction outweighed the risks of taking action," said Vaez.
"Tehran no doubt is aware of the risks in not only repeating but expanding its missile barrage it rained on Israel, thereby inviting an Israeli retaliation that seems all but certain to follow," he added.
Big Attack, Big Response
Iran's missile and drone attack on Israel in April, Tehran's first-ever direct assault on its foe, was highly telegraphed. Iran also used long-range drones and older missiles in that attack.
In comparison, Iran's October 1 attack was "very substantial," said Fabian Hinz, research fellow at the International Institute for Strategic Studies in London.
People stand on top of the remains of an Iranian missile in the Negev desert near Arad, Israel on October 2.
Preliminary evidence, he told RFE/RL's Radio Farda, suggests that Iran used ballistic missiles, which reached Israel in just minutes. The likely goal, Hinz says, was to give Israel limited time to prepare.
In April, Israel responded to Iran's attack by hitting an air-defense radar system in the central Iranian city of Isfahan.
But experts warn that Israeli retaliation is likely to be more severe this time.
Media reports citing Israeli officials said the country could strike strategic sites inside Iran, including energy facilities.
SEE ALSO: 'When Iran Is Finally Freed': Netanyahu's Video Message Goes Viral On Persian Social MediaA possible Israeli strike on an oil or gas facility in energy-rich Iran would be optically spectacular, but not strategically damaging, said Farzin Nadimi, senior fellow at the Washington Institute for Near East Studies.
Hitting a nuclear facility, Nadimi told Radio Farda, would be riskier and require a large attack, considering that Iran's key nuclear infrastructure is deep underground.
Strikes targeting Iran's nuclear facilities, which Israel and the United States have reportedly rehearsed, could push Tehran to weaponize its nuclear program, experts have warned.
"Regardless of [Israel's] target, such a blow is bound to compel Tehran to retaliate, triggering a ballistic missile ping-pong that could push the entire region into an abyss," Vaez said.