China firmly opposes and strongly condemns the killing of Iran's Supreme Leader Ayatollah Ali Khamenei, the Chinese Foreign Ministry said on Sunday.

"The attack and killing of Iran's supreme leader is a grave violation of Iran's sovereignty and security. It tramples on the purposes and principles of the UN Charter and basic norms in international relations," said a spokesperson for the ministry in a statement.

"China firmly opposes and strongly condemns it. We urge for an immediate stop to the military operations, no further escalation of the tense situation and joint efforts to maintain peace and stability in the Middle East and the world at large," the spokesperson added.