Beijing is a close 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, meeting top officials across the region this month.

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

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