Regime change in Iran is "unacceptable" and the assassination of the country's supreme leader would "open the Pandora's box", the Kremlin has said.

Axar.az reports in a rare interview with a foreign media organisation, Kremlin spokesman Dmitry Peskov told Sky News that Russia would react "very negatively" if Ayatollah Ali Khamenei was killed.

"The situation is extremely tense and is dangerous not only for the region but globally," Mr Peskov said in an interview at the Constantine Palace in Saint Petersburg.

"An enlargement of the composition of the participants of the conflict is potentially even more dangerous.

"It will lead only to another circle of confrontation and escalation of tension in the region."

Russia has deepened its ties with Iran since invading Ukraine, and the two countries signed a strategic partnership in January.

"[Regime change in Iran] is unimaginable. It should be unacceptable, even talking about that should be unacceptable for everyone," Mr Peskov said, in a thinly veiled reference to Washington.

But Mr Peskov refused to be drawn on what action Russia would take if Khamenei was killed, saying instead it would trigger action "from inside Iran".

"It would lead to the birth of extremist moods inside Iran and those who are speaking about [killing Khamenei], they should keep it in mind. They will open the Pandora's box."

Vladimir Putin's offers to mediate an end to the conflict have so far been rejected by Mr Trump, who said on Wednesday that he told the Russian president to "mediate your own [conflict]", in reference to Russia's war against Ukraine.

Mr Peskov denied the American president's words were insulting, adding: "Everyone has a different language.

"President Trump has his own unique way of speaking and his unique language. We are quite tolerant and expect everyone to be tolerant of us."