Iranian institutions and politicians, from the foreign ministry to lawmakers, issued statements expressing their allegiance to the country's new supreme leader as the war entered its 10th day and fresh missile and drone strikes reverberated across the Middle East.
"We will obey the commander-in-chief until the last drop of our blood," a statement from the defence council said.
Senior cleric Ayatollah Sadeq Amoli-Larijani said Mojtaba Khamenei's appointment was "a balm for the spiritual suffering of our people and an emphasis on the need to continue the luminous path of the late Imam (Khamenei senior)".
Mojtaba's father, Supreme Leader Ali Khamenei, was killed in one of the first strikes launched against Iran more than a week ago.
The show of solidarity for Mojtaba comes after US President Donald Trump earlier rejected him as a candidate to be Iran's new supreme leader, and Israel saying it would target whoever leads Iran.
Mojtaba, a cleric with influence inside Iran's security forces and vast business networks under his father, had been viewed as a frontrunner in the lead-up to Sunday's vote by the Assembly of Experts, a body of 88 clerics tasked with choosing Ali Khamenei's successor.
Trump said on Sunday Washington should have a say in the selection.
"If he doesn't get approval from us, he's not going to last long," he told US ABC News, adding that ending the war would be a "mutual" decision with Israeli Prime Minister Benjamin Netanyahu.
In an interview with the Times of Israel after the new supreme leader was named, Trump declined to respond, saying only "we'll see what happens".
The Israeli military said on Monday it had begun a wave of attacks in central Iran and had struck infrastructure belonging to Hezbollah militants in Beirut.
Iran and its proxies appeared to have launched attacks across the region too, with rocket and drone strikes targeting a US diplomatic facility near Baghdad's international airport that were intercepted by C-RAM defence system, police sources said.
A drone strike targeted a US military base near Erbil airport in Iraqi Kurdistan, security sources said, while Saudi authorities reported intercepting a drone near its Jawf region.
Thick smoke was seen rising from the direction of the BAPCO oil refinery in Bahrain, according to a Reuters witness, after the government said an Iranian drone strike hit the area, causing injuries and damage.
The US military reported a seventh American had died from wounds sustained during Iran's initial counter-attack a week ago, a day after Trump presided over the return to the US of the remains of the six others killed.
The Israeli military said on Sunday two of its soldiers were killed in southern Lebanon, marking the first fatalities among its troops since Israel-Hezbollah hostilities resumed last week as Israel intensified air strikes on Lebanon.
At least four people were killed when an Israeli strike hit an apartment in the Ramada hotel building in central Beirut early on Sunday.
The US-Israeli attacks have killed at least 1332 Iranian civilians and wounded thousands, according to Iran's UN ambassador.
US crude futures rose more than 20 per cent in early trade on Monday, hitting their highest since July 2022, as major Middle Eastern oil producers cut supply because they cannot safely send shipments through the Strait of Hormuz to refiners worldwide.
The war has forced production stoppages by oil and gas exporters from Qatar to Iraq, with Kuwait announcing cuts at the weekend and analysts predicting the UAE and Saudi Arabia will soon cut output as they run out of oil storage.
