Mojtaba Khamenei was himself wounded, according to statements by some Iranian officials and state television, but there remains uncertainty over his whereabouts and physical condition.
Here are five takeaways from his first statement as supreme leader.
Uncertainty over condition
"The first message of the supreme leader of the Islamic revolution, his excellency Ayatollah Seyyed Mojtaba Hossein Khamenei!" an Iranian TV anchor declared before reading out the lengthy statement.
There was, however, no attempt to end the speculation over Khamenei's condition, and the statement was not accompanied by video or audio of the new leader giving the remarks, or even a new still image.
Instead, the statement was read against the backdrop of an archive photo of Khamanei and a computer-generated flag of the Islamic republic.
Call for revenge
In the statement, Khamenei offered no hint that he was seeking to make peace with Iran's enemies, and instead emphasised his desire for revenge in a war that has claimed the life of his father and his wife.
"A limited amount of this revenge has so far taken concrete form, but until it is fully achieved, this case will remain among our priorities," Khamenei said.
"We will seek compensation from the enemy, and if they refuse, we will take as much of their property as we determine, and if that is not possible, we will destroy the same amount of his property," he added.
He singled out a deadly strike on a school in Minab in southern Iran that Iranian authorities have said was carried out by the US and left 150 people dead, describing it as a "crime the enemy deliberately committed".
A preliminary US military investigation has determined that a missile struck the school because of a targeting mistake, The New York Times reported on Wednesday.
Threats to enemies
Echoing the language of his late father, Khamanei also emphasised Iran's potential to cause havoc across the region by squeezing oil supplies and using regional proxies.
He called for using "the lever of blocking the Strait of Hormuz" -- a strategic waterway through which a fifth of global oil passes.
"The will of the people is for the continuation of an effective and deterrent defence that will make the enemy regret its actions."
He warned that "studies have also been carried out on opening other fronts in which the enemy has little experience and in which it will be extremely vulnerable", without giving details.
Those fronts would be "activated" if the war continued, he said.
Warning to region
Khamenei noted that Iran shared land or sea borders with some 15 countries and "we have always desired warm and constructive relations" with these neighbours.
But Khamenei called for the closure of US bases in nearby countries, saying "the claim of establishing security and peace by America was nothing more than a lie".
"These countries must determine their stance regarding those who have invaded our dear homeland and killed our people."
Grieving son and husband
He lauded his father as a "shining treasure and distinguished figure in history", and said he had seen the late ayatollah's corpse after his "martyrdom".
Khamenei described the body as "a mountain of steadfastness" with the fist of his father's one functioning hand -- his other arm was paralysed after a bomb attack in the 1980s -- clenched in a sign of defiance.
Khamenei emphasised that as well as his father, he had also lost in the attack "my dear and loyal wife", his sister, her child and his brother-in-law.
He did not mention his mother, who previous reports said had also been killed. The Fars news agency said Thursday those reports were inaccurate and she was still alive.
Khamenei said that he had learned of his appointment by the Assembly of Experts clerical body "at the same time as you" on television through the state broadcaster.
