Attending a summit meeting of Caspian Sea states, Mr Putin, along with three other signatories, also agreed never to allow their territory to be used for an attack on a fellow littoral state.

Azerbaijan, Kazakhstan and Turkmenistan, the other countries attending the summit, along with Russia and Iran, also backed the right of Non-Proliferation Treaty members to 'research, produce and use nuclear energy for peaceful ends, without discrimination, within the framework of this treaty and the mechanisms of the UN nuclear watchdog'.

Mr Putin is the first Kremlin chief to visit Iran since World War II. His support for Iran's nuclear programme is a shot in the arm for Teheran, which is currently embroiled in a face-off with the West. The US claims that Iran's nuclear energy programme is only a cover for its atomic weapons drive.

The claims have also given rise to continued speculation over the possibility of a US military strike against Iran.

'The (Caspian) parties emphasise that in no circumstances will they allow their territory to be used by a third country to commit aggression or other military action against one of the parties,' the declaration said.

Russia is seeking diplomacy over the West's insistence on United Nations sanctions to punish Teheran for its defiance on the nuclear programme.

The former superpower has said it is not convinced by Western claims that the nuclear programme is military in nature. Teheran insists the atomic drive is entirely peaceful.

'Russia is the only country helping Iran to construct a nuclear power station for peaceful ends,' Mr Putin said, referring to the still unfinished project to build Iran's first nuclear energy plant in Bushehr.

Earlier, Russian news agencies had reported an assassination threat, but Mr Putin had insisted that he would 'of course' press ahead with his visit.

His travel plans were kept under wraps, and his plane landed at Teheran's Mehrabad airport early yesterday morning. Iranian media reported that Mr Putin's armour-plated car had been air-freighted into Teheran ahead of his visit to ensure his security.

Mr Putin was to meet Iranian President Mahmoud Ahmadinejad and supreme leader Ayatollah Ali Khamenei later.

AGENCE FRANCE-PRESSE