Iran's Supreme Leader Ali Khamenei said in a statement on Friday that Israel initiated a war and said it will not be allowed to do "hit and run" attacks without grave consequences.

"The Zionist regime (Israel) will not remain unscathed from the consequences of its crime. The Iranian nation must be guaranteed that our response will not be half-measured," Khamenei said in a statement.

Israel launched blistering attacks on the heart of Iran's nuclear and military structure Friday, deploying warplanes and drones previously smuggled into the country to attack key facilities and kill top generals and scientists -- a barrage it said was necessary before its adversary got any closer to building an atomic weapon.

Iran’s state news agency reported that Iran fired hundreds of ballistic missiles toward Israel as part of its retaliation for Israel's Friday attack.

IRNA said the Iranian military had dubbed its operation "Severe Punishment."

Explosions were heard over Tel Aviv and Jerusalem as sirens sounded across Israel following what the country's military spokesman said was the firing of missiles from Iran. 

The ongoing military and intelligence operation raised the potential for all-out war between Iran and Israel and propelled the region, already on edge, into even greater upheaval.