Russia is prepared to invest $50bn in Iran’s energy sector, according to Ali Akbar Velayati, a senior adviser to Iran’s supreme leader.

The announcement follows the US decision to reimpose sanctions on Tehran.

"Russia is ready to invest $50bn in Iran’s oil and gas sectors," Velayati told the Financial Times during a visit to Moscow that included a meeting with President Vladimir Putin.

"Military and technical cooperation with Russia is of major importance to Iran."

Velayati is Ayatollah Ali Khamenei’s top diplomat.

During his trip to Moscow he used a media interview to say that a Russian oil company had already signed a $4bn deal with Iran that "will be implemented soon", without providing details.

He also said: "Two other major Russian oil companies, Rosneft and Gazprom, have started talks with Iran’s oil ministry to sign contracts worth up to $10bn."

On 13 July Russia’s energy minister Alexander Novak said that Moscow is interested in developing an oil-for-goods programme. This would allow Iranian companies to buy Russian products in exchange for oil contracts that could be sold to other countries.

US President Donald Trump announced American withdrawal from the 2015 nuclear agreement on 8 May, making the return of US sanctions on Iran almost inevitable.

While many of these sanctions are due to return on 6 August, penalties focusing on oil will return 90 days later, on 4 November.