An Iranian state television broadcast has been bombed live on air as Israel and Iran stepped up missile attacks against each other.
Explosions were seen ringing out in the Iranian capital of Tehran, where residents could be seen joining huge queues of traffic trying to leave on Monday.
From the G7 summit in Canada, Mr Trump posted an urgent warning.
"Iran should have signed the 'deal' I told them to sign. What a shame, and waste of human life. … I said it over and over again!" he said.
"Everyone should immediately evacuate Tehran!"
The message came just moments before the White House announced Mr Trump would be leaving the summit and returning to the White House "because of what's going on in the Middle East".
At least 224 people had been killed in Iran by Israeli strikes between Friday and Sunday, amid reports Iran had reached out to the US to indicate its desire for a ceasefire.
Meanwhile, the death toll in Israel has risen to 24 since the conflict began, as Iran continued its retaliatory strikes.
On Monday evening local time, further missile alerts sounded in northern Israel as Iran vowed to "pummel" the country until Israel stopped launching attacks.
At the scene of a deadly strike in the Israeli city of Petah Tikva, residents were gathering essentials and preparing to move out of their apartments.
"Our home is in a bad situation, you can't live in it," Liel Fenigshtein, who lives in the adjacent building, told the ABC.
"We can't drive our cars or wear our clothes. We don't have anything."
She and other residents described being stuck in their homes after the blast, because of the extensive damage.
Locals say war 'necessary' despite toll
Another neighbour, Matthew Danoff, described the explosion as a "huge boom", shaking all the apartment towers.
"I've been here [Israel] for the past 10 years … and I've never seen anything like this before. This is crazy and I want it to stop. I hope it stops soon," he said.
"I'm just super grateful that we're OK but I feel bad for the people who were in the building next to us because they did everything they could. They were in the mamad [safe room], they were in the bomb shelter, they followed protocol. It's just an unfortunate situation."
But Mr Danoff and other residents said they supported Israel's decision to attack Iran, even though it meant they were affected by the Iranian retaliation.
"I think honestly that it's something that we have to do, unfortunately. It's a really shitty situation, but I think Iran having that nuclear capability is a lot worse," he said.
"But I think it's a step in the right direction and I know it's a very unpopular opinion, but for my sake and Australia's sake and the rest of the western world's sake, I think it's what we have to do."
Mr Danoff said he doubted Iran had deliberately targeted the apartment towers, but was instead firing at population centres.
"I think it was really like a 'spray and pay' sort of method and unfortunately hit this building. They don't care about casualties, they were just firing wherever," he said.
Iran's military has said it is targeting military sites and energy infrastructure in retaliation for Israeli strikes on its oil and gas facilities.
Another neighbour, Yafit Bareket, said her home across the road from the affected building had also suffered major damage. She also expressed support for Israel's campaign.
"We are strong, our spirit is strong. We will win, we will fight, we are not afraid of the terrorists. And you will see, Israel will be number one," she told the ABC.
"I believe in Prime Minister Benjamin Netanyahu that he made the best thing for the state of Israel.
"But we are smiling and our spirit is strong. They cannot break us."
Israel attacks Iranian state media
As Israeli residents cleaned up, the country's military said it had established full aerial dominance in the skies over Iran.
The Israel Defense Forces also claimed to have destroyed Iranian aircraft at Tehran airport, while Iran state media said its air defences had downed an Israeli F35.
Israel's strikes have so far killed top military commanders, nuclear scientists and civilians, according to Iranian authorities.
On Monday, Israel's government urged residents in a part of Tehran to evacuate, before launching strikes against Iran's state broadcaster.
Footage showed a newsreader ducking for cover and running off screen as debris fell in the studio she was presenting from.
The live feed of Islamic Republic of Iran Broadcasting (IRIB) was abruptly cut but resumed broadcasting shortly afterwards.
Iranian Foreign Ministry spokesperson Esmaeil Baqaei accused Israel of committing a war crime by launching the strikes at the broadcaster.
Israeli Defence Minister Israel Katz said that "the propaganda and incitement broadcasting authority of the Iranian regime was attacked", threatening to strike "everywhere" against "the Iranian dictator".
Netanyahu says killing Iranian supreme leader would 'end the conflict'
Meanwhile, Israeli Prime Minister Benjamin Netanyahu was again asked about reports Donald Trump vetoed a plan to assassinate Iran's supreme leader, Iran's supreme leader Ayatollah Ali Khamenei.
Mr Netanyahu told ABC America such a step was "not going to escalate the conflict, it's going to end the conflict".
"The 'forever war' is what Iran wants, and they're bringing us to the brink of nuclear war," he said.
"In fact, what Israel is doing is preventing this, bringing an end to this aggression, and we can only do so by standing up to the forces of evil."
Iran launches fresh strikes
After a series of strikes against Tehran, Iran vowed swift retaliation on Monday night.
Iran's state TV issued threats against Israeli broadcasters N12 and N14 in retaliation, and later announced a fresh salvo of missile and drone strikes had been launched against Israel.
Israeli citizens received emergency alerts several times on Monday night local time.
A spokesperson for Iran's Revolutionary Guards said strikes would continue against Israel until morning.
After an Iranian strike damaged a power plant in Haifa, Israel's Energy Ministry said other generators would be able to provide enough power to keep lights on across the country.
ABC/wires
