Israel's massive strikes on Iran, which it calls an existential threat, have hit nuclear and military facilities, killed top commanders and dozens of civilians, and sought to destroy the country's defence capabilities.

Iran called the Israeli air assault "a declaration of war" and fired dozens of missiles at Israel later Friday and Saturday.

Despite the Israeli strikes, the US president has urged Tehran to comply with Washington’s demands over its nuclear program “before it is too late”

Iran's Supreme Leader Ayatollah Ali Khamenei is alive and is being continuously briefed about the situation, a security source told Reuters, following an Israeli attack on Iran early on Friday.

Pakistan strongly condemned Israel’s military strikes on Iran, calling them a blatant violation of international law and Iran’s sovereignty. Islamabad urged the United Nations and the global community to intervene and prevent further escalation in the region.

Oil prices soared more than 12 percent and stocks sank Friday after Israel launched strikes on Iranian nuclear and military sites and warned of more to come, stoking fears of a full-blown war.

Israel pounded Iran in a series of air raids on Friday, striking 100 targets including Tehran's nuclear and military sites, and killing the armed forces' chief of staff, the head of Iran's Revolutionary Guards and top nuclear scientists.

Iran's Revolutionary Guards chief Hossein Salami, who was killed in an Israeli air strike on Tehran Friday, was a veteran officer close to supreme leader Ayatollah Ali Khamenei known for his tirades against Israel and its US ally.

Middle East leaders and their Western allies have been warning that ISIS could exploit the fall of the Assad regime to stage a comeback in Syria and neighbouring Iraq, where the extremist group once imposed a reign of terror over millions.

Iran's top diplomat and chief nuclear negotiator will meet the head of the International Atomic Energy Agency in Cairo on Monday, Egypt's foreign ministry said.

Saudi Arabia’s defense minister delivered a blunt message to Iranian officials in Tehran last month: Take US President Donald Trump’s offer to negotiate a nuclear agreement seriously, because it presents a way to avoid the risk of war with Israel.

An adviser to supreme leader Ayatollah Ali Khamenei said Wednesday that Iran could accept far-reaching curbs on its nuclear program in exchange for sanctions relief, US media reported.