Iran has touted $50bn worth of potential Russian investments in its oil and gas sector as it seeks to deepen its relationship with Moscow, amid mounting pressure from the US to curb the country’s energy exports and diplomatically isolate Tehran. Russia has sought to use its vast oil and gas industry to build stronger links with Iran, as part of a strategy to increase its role in the Middle East.

This includes supporting the government of Bashar al-Assad in the Syrian war, as relations with the west sour and US sanctions force it to look for new trade and investment partners.

“Russia is ready to invest $50bn in Iran’s oil and gas sectors,” Ali Akbar Velayati, a senior adviser to Iran’s supreme leader, said during a visit to Moscow that included a meeting with President Vladimir Putin. “Military and technical co-operation with Russia is of major importance to Iran.”

Russia’s relationship with Iran is likely to be a key element of talks between Mr Putin and US president Donald Trump in Helsinki on Monday. Mr Trump is expected to demand that Mr Putin move to curb Iranian influence in Syria, and may threaten further sanctions if Russian companies continue doing business with Tehran, according to FT.com.

Mr Velayati, Ayatollah Ali Khamenei’s top diplomat, also used a media interview during his visit to say that a Russian oil company had already signed a $4bn deal with Iran that “will be implemented soon”, without providing details.

He added: “Two other major Russian oil companies, Rosneft and Gazprom, have started talks with Iran’s oil ministry to sign contracts worth up to $10bn.” A Russian government official confirmed the $50bn investment plans on condition of anonymity.