Israel unleashed a punishing barrage of strikes across Iran on Sunday, hitting targets from the west to Tehran and as far east as Mashhad, after Prime Minister Benjamin Netanyahu vowed to make the country pay a “heavy price” for killing civilians.

Investors have been weighing the odds of further escalation in the conflict and spillover into the broader oil-rich Middle East.

Sirens sounded in Israel as Iran launched dozens of ballistic missiles in retaliation for Israel's strikes on its nuclear facilities.

Iran is planning to 'give a harsh response' to an Israeli attack launched early on Friday against its nuclear programme, an Iranian security source told Reuters.

"The full strength and might of the U.S. Armed Forces will come down on you at levels never seen before," Trump warned.

In all, at least 20 senior commanders were killed, two regional sources said. The head of the Revolutionary Guards aerospace force was also reported to be among them.