"In response to months of continuous attacks from the regime in Iran against the State of Israel –- right now the Israel Defense Forces [IDF] is conducting precise strikes on military targets in Iran," the military said in a statement.

Israel had vowed to hit back at Iran following its Oct. 1 missile attack, with Defense Minister Yoav Gallant saying the response would be "deadly, precise and surprising".

Israel has been fighting Iran-backed Hamas in Gaza since the deadliest attack in its history on Oct. 7, 2023, which killed 1,206 people, mostly civilians, according to an AFP tally of official Israeli figures. 

It has since broadened the scope of its operations to Lebanon, vowing to secure its northern border after nearly a year of attacks launched by Iran-backed Hezbollah in support of Hamas.

"Our defensive and offensive capabilities are fully mobilized," the Israeli military said in a statement. 

Military spokesman Daniel Hagari in a separate statement urged people to be "alert and vigilant".

Iran's Oct. 1 strike, its second direct attack on Israel, came after an Israeli air raid killed Hezbollah chief Hassan Nasrallah and Revolutionary Guards general Abbas Nilforoushan in Lebanon on September 27.

It also followed the killing of Hamas's political leader, Ismail Haniyeh, on July 31 in Tehran in an attack widely blamed on Israel.

The rapid escalation of violence has raised fears across the region of a wider war, pitting Israel against Iran and the allies it dubs the "axis of resistance".

'Fully mobilized'

Iranian state television said Saturday "strong explosions" were heard around the capital, though it did not specify the cause of the blasts.

"Minutes ago, the sound of strong explosions were heard from around Tehran, the source of these sounds is not yet clear," a state TV presenter said. 

It later said "six loud blasts" were heard in areas of Tehran.

An AFP reporter also heard the explosions.

Iranian media said no fire or explosions had been reported at a main oil refinery near the capital.

Iran had in recent weeks warned that any attack on its "infrastructure" would provoke an "even stronger response", while Revolutionary Guards general Rassul Sanairad said an attack on nuclear or energy sites would cross a red line.

United States National Security Council spokesman Sean Savett said the "targeted strikes on military targets" are "an exercise of self-defense and in response to Iran's ballistic missile attack against Israel on Oct. 1."

The United States was "informed beforehand and there is no US involvement," a US defense official told AFP, on condition of anonymity.

The official did not say how far in advance the United States had been informed or what had been shared by Israel.

The scope and nature of Saturday's strike was not immediately clear, but in a possible indication, Syrian state news agency SANA said Syrian air defenses had intercepted what it described as "hostile targets" near the capital city, Damascus.

"Our anti-aircraft defense is confronting hostile targets in the skies around Damascus," SANA said on Telegram. 

It also reported "sounds of explosions" in the vicinity of Damascus, though the origin of those blasts was unclear.