Iran's supreme leader Ayatollah Ali Khamenei on Tuesday called for strengthening "long-term cooperation" with Russia in a meeting with visiting Russian President Vladimir Putin, a statement said.

"The long-term cooperation between Iran and Russia is deeply beneficial to both countries," Khamenei said, according to a statement on his official website.

"There are many understandings and contracts between the two countries, including in the oil and gas sector, which must be followed up and implemented fully," Khamenei added.

He said world events showed the need for ever-increasing mutual cooperation between the two countries, "especially in the wake of Western sanctions", the statement read.

Putin arrived in Tehran earlier in the day for talks on the Syrian war at a three-way summit with the Iranian and Turkish presidents that has been overshadowed by fallout from Russia's invasion of Ukraine.

It is Putin's second trip abroad since ordering the invasion in late February.

Khamenei told Putin that although Iran "is not at all happy that ordinary people" are suffering from the Ukraine war, the West was to blame.

"If you did not take the initiative, the other side would have caused the war with its own initiative," Khamenei said.

Prior to Putin's visit, the National Iranian Oil Company and Russia's Gazprom signed a memorandum of understanding "worth about $40 billion", the Iranian oil ministry's official news agency Shana reported.

Gazprom said the MoU looks to "analyse possibilities of cooperation" in different areas, including development of Iran's gas and oil fields.

Earlier on Tuesday, Putin met his Iranian counterpart Ebrahim Raisi, discussing bilateral relations and the Syria conflict.

"We are strengthening our international security cooperation and making a significant contribution to resolving the Syrian crisis," Putin told Raisi, according to a statement on the Kremlin website.