Israel and Iran traded heavy fire for a third straight day on Sunday, with mounting casualties and expanding targets marking a sharp escalation in hostilities between the longtime foes.

Strikes in both countries persisted throughout the day, as the death toll rose following Israel's large-scale attacks on Friday aimed at crippling Iran's nuclear and military infrastructure, sparking retaliation.

The intensity of the exchanges fueled concerns of a drawn-out conflict that could engulf the Middle East, even as world leaders call for an end to the violence.

Here are the latest developments:

Rising death tolls

Death tolls mounted on both sides, as strikes hit residential areas.

Iran unleashed waves of missiles at Israel at the weekend, killing 10 people, including children, and bringing the overall toll to 13 dead and 380 wounded.

Israeli Prime Minister Benjamin Netanyahu vowed to make Iran pay "a very heavy price" for the civilian deaths.

Sirens sounded again in multiple areas of Israel in the afternoon as Iran launched a new barrage.

Israeli attacks on Iran killed at least 224 people since Friday, including children, Iranian media reported, citing the health ministry, with hundreds more wounded.

Iran opened mosques, metro stations and schools as shelters for citizens from Israel attacks, as the Israeli military warned Iranians to leave areas near weapons facilities. 

Expanding targets

The Israeli military said Sunday it had hit more than 80 targets in Tehran overnight, as its attacks expanded from Iranian military and nuclear facilities, as well as killing top commanders and scientists, to hit also oil and government sites. 

Israeli strikes hit two fuel depots in Tehran on Sunday. It also struck Ahvaz, in the oil-rich southwestern province of Khuzestan, said Mehr news agency.

Iranian media on Sunday reported Israel had targeted Tehran's police and defense ministry headquarters and a ministry-affiliated facility in Isfahan. 

Iran struck sites used by Israeli warplanes for refueling, said the Revolutionary Guards.

Israel said it had intercepted seven drones, as Yemen's Iran-backed Huthi rebels said they also fired missiles at Israel on Sunday.

Its military said later it hit Mashhad airport in Iran's far east in its longest-distance strike yet, as well as other targets across the country, including the capital.

Iranian state television said at least five people had been killed in a strike on a residential building in downtown Tehran.

A senior Iranian military official on Sunday warned of a "devastating response" to Israeli attacks on the Islamic republic, adding that Israel would not be habitable as a result.

Faltering nuclear diplomacy

The fierce exchanges of fire came amid talks between Tehran and Washington seeking to reach a deal on Iran's nuclear program.

Western governments have repeatedly accused Iran of seeking a nuclear weapon, which it denies.

The sixth round of negotiations set for Sunday in Oman have been called off. Tehran said it would not attend talks with Washington as long as Israel kept up its attacks.

Iranian Foreign Minister Abbas Araghchi on Sunday hit out at Israel, saying its attacks were an "attempt to undermine diplomacy and derail negotiations".

Araghchi also accused Israel of having "crossed a new red line" by targeting Iran's nuclear sites.

Tehran has accused the UN nuclear watchdog of inaction over the Israeli strikes and pledged to limit cooperation with the agency.

Mediators Qatar and Oman were told by Iran that Tehran "will not negotiate while under attack", an official briefed on the talks said Sunday.

International unease

Countries have voiced growing alarm over the conflict spilling into the wider region, calling for de-escalation.

Araghchi on Sunday slammed one of Israel's strikes on a major gas facility along the Gulf coast, saying any military activity in the key waters "could involve the entire region -- and possibly the whole world". 

He said Tehran had "solid proof" that US forces and bases in the region had supported Israel in its attacks.

Washington -- a top Israel ally and Tehran rival -- has denied involvement and called for an end to the exchanges of fire, with President Donald Trump on Sunday reiterating a call for the two sides to "make a deal".

Trump said later told ABC television the United States "could get involved" in the conflict.

And, according to a US official, he also prevented an Israeli plan to assassinate Iran's supreme leader, Ayatollah Ali Khamenei.

Netanyahu, speaking to Fox News, said however that Israel "got the chief intelligence officer and his deputy in Tehran". Iran said later an Israeli strike killed Revolutionary Guards intelligence chief Mohammed Kazemi, along with two other officers.