China firmly opposes and strongly condemns the attack and killing of Iran's Supreme Leader Ayatollah Ali Khamenei by the United States and Israel in the air strikes, a Foreign Ministry spokesperson said on Sunday.

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Calling such an act a grave violation of Iran's sovereignty and security, the spokesperson said it also tramples on the purposes and principles of the United Nations Charter and basic norms in international relations.

"We urge an immediate stop to the military operations, no further escalation of the tense situation and joint effort to maintain peace and stability in the Middle East and the world at large," the spokesperson added.