Iran's Foreign Ministry said in a Sunday statement that Supreme Leader Ali Khamenei had become "an inspiring legend in the history of Iran and Islam" following his killing in the U.S.-Israeli attack on Tehran on Saturday.

Khamenei, the statement on X said, "lived a pious life, loved Iran, secured Iran's independence, opposed foreign domination and worked tirelessly for our country's resilience and fortitude."

He died, the ministry said, "at the hands of the most corrupt and criminal individuals on earth." Khamenei, the statement added, "will remain a living nightmare for his killers forever."

Hundreds of protesters stormed the U.S. consulate in Karachi -- Pakistan's largest city on the country's southern coast -- on Sunday to protest the killing of Iranian Supreme Leader Ayatollah Ali Khamenei.

At least six protesters were killed in the clashes, local authorities said. Police used tear gas to disperse the demonstration.

In a post to X, the U.S. Embassy in the capital Islamabad said it was "monitoring reports of ongoing demonstrations at the U.S. Consulates General in Karachi and Lahore, as well as calls for additional demonstrations at U.S. Embassy Islamabad and Consulate General Peshawar."

"We advise U.S. citizens in Pakistan to monitor local news and observe good personal security practices, including being aware of your surroundings, avoiding large crowds and ensuring your STEP registration is up to date," it added.

-ABC News' Habibullah Khan and Ellie Kaufman

Iranian President Masoud Pezeshkian issued a statement on Sunday morning saying that Supreme Leader Ali Khamenei was "martyred at the hands of the most wicked villains in the world."

"The assassination of the highest political official of the Islamic Republic of Iran and the prominent leader and authority of the Shiite world by the sinister American-Zionist axis is considered a declaration of open war on Muslims, especially Shiites, in all corners of the world," Pezeshkian said.

"The Islamic Republic of Iran considers bloodshed and revenge against the perpetrators and commanders of this historical crime as its legitimate duty and right, and will do its utmost to fulfil this great responsibility and duty," Pezeshkian said.

-ABC News' Somayeh Malekian and Victoria Beaule

Ali Larijani, the secretary of the Supreme National Security Council of Iran, appeared in a television interview on Sunday to mourn killed Supreme Leader Ali Khamenei and vow retaliation against the U.S.

"The passing of a great personality has wounded the hearts of all of us," Larijani said, adding that, "Americans should know that by stabbing the hearts of the Iranian nation, their hearts will be stabbed."

"What they did in a cruel way towards the Iranian leadership has angered the people so much that they will never achieve their goals," he said.

Larijani added that a temporary leadership council would be formed consisting of the president, the head of the judiciary and one of the jurists of the Guardian Council.

Larijani also posted to X on Sunday morning saying that Saturday's attacks on Iran "did hurt" but that Iran would hit the U.S. and Israel "with a force they have never experienced before."

-ABC News' Somayeh Malekian and Victoria Beaule