A senior Russian official said on Sunday that US President Donald Trump had started a new war by attacking Iran that would only strengthen Tehran's leaders by consolidating society around Supreme Leader Ali Khamenei.

The Kremlin, which has a strategic partnership with Iran and also maintains close links to Israel, had repeatedly cautioned Washington that US strikes on Iran would plunge the entire region into the "abyss".

"Trump, who came in as a peacemaker president, has started a new war for the US," said Dmitry Medvedev, the deputy chairman of Russia's Security Council, adding that "with this kind of success, Trump won't win the Nobel Peace Prize".

"Iran's political regime has been preserved and it is highly likely that it has become stronger," Medvedev said. "The people are consolidating around the spiritual leadership, even those who did not sympathise with it."

Medvedev also said that Iran's nuclear infrastructure did not appear to be affected by the US strikes, and that the US was in danger of being drawn into a ground operation.

President Vladimir Putin had repeatedly offered to mediate between the United States and Iran, though the Kremlin chief last week refused to discuss the possibility that Israel and the United States would kill Khamenei.

Putin said that Israel had given Moscow assurances that Russian specialists helping to build two more reactors at the Bushehr nuclear power plant in Iran would not be hurt in air strikes.

Russia's foreign ministry strongly condemned the US attacks which it said had undermined the Treaty on the Non-Proliferation of Nuclear Weapons. The United Nations Security Council must respond, Moscow said.

"It is already obvious that a dangerous escalation has begun, fraught with further undermining of regional and global security," it said. "The risk of the conflict spreading in the Middle East, which is already gripped by multiple crises, has increased significantly."

While Moscow has bought weapons from Iran for its war in Ukraine and signed a 20-year strategic partnership deal with Tehran earlier this year, their relationship since the 16th century, when Muscovy officially established relations with the Persian Empire, has at times been troubled.

Inside Russia, there were calls for Russia to come to the aid of its partner and to supply Iran with the same support which Washington had given to Ukraine - including air defence systems, missiles and satellite intelligence.

"It's time for us to help Tehran," said Russian businessman Konstantin Malofeyev. "And at the same time, to offer the United States and Iran diplomatic assistance in peace negotiations by appointing a special envoy for this. Two can play at this game."

Jailed Russian nationalist Igor Girkin said that unless Russia supported Iran, the Islamic Republic would be bombed into the Stone Age by the United States and Israel and then plunged into chaos.