Beijing is a partner of Iran but has also criticised Tehran's strikes against Gulf states housing US military bases.

Larijani was the highest-profile Iranian killed since supreme leader Ali Khamenei and other senior figures died during a wave of US and Israeli strikes when the war started on February 28.

"We have always opposed the use of force in international relations. The acts of killing Iranian state leaders and attacking civilian targets are even more unacceptable," China's foreign ministry spokesman Lin Jian told a news conference when asked about Larijani's death.

"China urges the parties concerned to immediately cease military operations and prevent the regional situation from spiralling out of control", Lin said.

Beijing has sought to mediate in the war, with its special envoy to the Middle East, Zhai Jun, travelling across the region this month to meet top officials.

His trip included stops in Saudi Arabia, the United Arab Emirates, Bahrain, Kuwait and Egypt.

Zhai emphasised during his visits that "non-military targets should not be attacked, and the safety of shipping lanes should not be disturbed", according to spokesman Lin.

The envoy's trips were "one part of China's intensive diplomatic efforts" in the Middle East, Lin said, adding that Beijing's "diplomatic mediation efforts will not cease as long as the conflict continues".

China's foreign ministry said this week that Beijing would provide humanitarian assistance to Iran, Lebanon, Jordan and Iraq.