TEHRAN -- Iran confirmed early Sunday that its Supreme Leader Ali Khamenei was killed in US-Israeli airstrikes here the previous day.

"Iran's leader attained martyrdom while carrying out his duties at his office," reported Iran's Nour News affiliated with the country's Supreme National Security Council.

The report said that the attack also resulted in the deaths of Khamenei's daughter, son-in-law, grandchild, and one of his daughters-in-law.

In response to the loss, the Iranian cabinet issued a statement declaring 40 days of national mourning, the official news agency IRNA reported.

The statement said Iran's leader was killed following a "brutal attack by the criminal US government and the sinister Israeli regime," praising Khamenei for having led the country "sagaciously" for more than 37 years.

The Iranian government vowed that the perpetrators of the "major crime" would be held accountable, and that Iran would ensure those responsible "regret their actions."

In line with constitutional procedures, Mohammad Mokhber, the Supreme Leader's aide, confirmed that the leadership duties would temporarily be assumed by Iran's president, judiciary chief, and a jurist from the Constitutional Council, as outlined in Article 111 of Iran's Constitution, the semi-official Tasnim News Agency reported.

The Islamic Revolutionary Guard Corps (IRGC), in a statement published on its official outlet, Sepah News, offered its condolences and vowed that the Iranian nation would exact "a hard, decisive, and regret-inducing" punishment on the "murderers." It denounced the U.S. and Israeli attack as a "criminal and terrorist" act that violated international norms.

Following the announcement of Khamenei's death, Iranian mourners took to the streets across various cities on Sunday, voicing their anger and calling for retribution.

Born in 1939, Khamenei became Iran's Supreme Leader in 1989 after the death of the Islamic Republic's founder, Ruhollah Khomeini.

On Saturday morning, the United States and Israel launched "major combat operations" against Iran. In retaliation, Iran launched missile and drone strikes targeting US and Israeli military installations across the West Asia region.