Here are the latest developments:

- Tehran again under attack -

Israel carried out "strikes of unprecedented force against regime targets and agencies of government oppression in the heart of Tehran", Defence Minister Israel Katz said as an AFP journalist heard loud blasts in the north of the capital.

Katz later said the targets included the notorious Evin prison in the city's north, known to hold political prisoners and dissidents as well as foreign detainees.

Iran's judiciary confirmed Evin was struck, reporting "damage" and stressing the situation was "under control".

Iran's Tasnim news agency said Israel also carried out a strike on the underground Fordo nuclear site, south of Tehran, already hit by US "bunker buster" bombs at the weekend.

The Israeli strikes on Monday hit a power supply system in Tehran, triggering outages in some areas, Fars news agency said.

In Israel, air raid sirens sent people to bomb shelters on Monday, with the military reporting at least three missile barrages in less than two hours.

Israeli media reported an impact in the area of the southern port of Ashdod.

The state power company reported disruptions in electricity supply "due damage near a strategic infrastructure facility" in Israel's south, without naming the location.

Israeli strikes on Iran since June 13 have killed more than 400 people, Iran's health ministry said. Iran's attacks on Israel have killed 24 people, according to official figures.

- 'Extension of war' -

Iran's armed forces threatened on Monday to inflict "serious, unpredictable consequences" on the United States in retaliation for its strikes on nuclear sites.

US warplanes hit Isfahan, Natanz and the Fordo facility in support of the Israeli bombardment campaign.

"This hostile act... will widen the scope of legitimate targets of the armed forces of the Islamic Republic of Iran and pave the way for the extension of war in the region," said armed forces spokesman Ebrahim Zolfaghari.

Ali Akbar Velayati, an adviser to Iran's supreme leader Ayatollah Ali Khamenei, said bases used by US forces "in the region or elsewhere" could be attacked.

The US State Department issued a "worldwide caution" for Americans on Sunday, and its embassy in Bahrain -- home to a major US military base -- reduced on-site staffing citing "heightened regional tensions".

- 'Spillover' -

China on Monday warned against "the spillover of war", urging the international community to do more to prevent the fighting from impacting the world's economy, noting the global importance of the Gulf maritime trade routes off the Iranian coast.

Oil prices briefly fell into the red on Monday after surging, as traders weighed possible retaliation by Iran.

US Secretary of State Marco Rubio called on China to help deter Iran from closing the Strait of Hormuz, a chokepoint for one-fifth of the world's oil supply.

The European Union's foreign policy chief, Kaja Kallas, said closing the strait would be "extremely dangerous".

Major oil producers Russia and Iraq expressed "concern" over volatility in world energy markets, the Kremlin said after a phone call between the leaders of the two countries.

- Trump claims 'monumental damage' -

Trump wrote on social media on Sunday that "Monumental Damage was done to all Nuclear sites in Iran, as shown by satellite images. Obliteration is an accurate term!" He did not share the images he was referencing.

US Joint Chiefs Chairman Dan Caine said seven B-2 stealth bombers had flown 18 hours to drop 14 GBU-57 bunker-buster bombs -- a powerful 13,600-kilo (30,000-pound) weapon.

The general said it was too soon to assess the impact on Iran's nuclear programme, which Tehran insists is not aimed at developing a bomb.

The UN's International Atomic Energy Agency said it had not detected any increase in radiation levels at key nuclear sites in Iran after the US strikes.

- Nuclear stockpiles -

The IAEA demanded Monday the return of inspectors to Iran's nuclear sites in a bid to "account for" its highly enriched uranium stockpiles.

"Allow IAEA inspectors... to go back to Iran's nuclear sites and account for the stockpiles of uranium" including the "400 kilograms enriched to 60 percent", said agency chief Rafael Grossi.

At an emergency meeting of the organisation's headquarters in Vienna, he said Tehran had sent him a letter on June 13 announcing the implementation of "special measures to protect nuclear equipment and materials".

burs-ami/dv