China will begin implementing a strategic agreement with Iran, aimed at improving economic and security co-operation, Beijing said on Saturday. The agreement will also cover energy and infrastructure projects. Billed as a 25-year, multi-sector agreement that would see as much as $400 billion worth of collaborative projects, the deal, which was signed last year, underlines China’s long-held opposition to US sanctions. Last year, Iran’s oil minister Javad Owji said Iran was seeking more than $145 billion in energy investment to bolster its oil industry over the next four to eight years. Chinese foreign minister Wang Yi and Iranian counterpart Hossein Amir-Abdollahian announced the start of the partnership's implementation at a meeting in east China's Wuxi on Friday, Beijing's foreign ministry said. According to China’s Ministry of Commerce, Beijing invested $3.41 billion in Iran in 2019, before the disruption of the global pandemic. Mr Wang told his Iranian counterpart on Friday that China would continue to "oppose illegal unilateral sanctions against Iran," the foreign ministry said. Beijing has long sought to boost ties with Tehran, with Chinese president Xi Jinping describing Iran as "China's major partner in the Middle East" on a rare visit to the country in 2016. Mr Wang and Mr Amir-Abdollahian's meeting comes as talks continue in Vienna over a potential deal to halt Tehran's development of nuclear weapons. A 2015 deal – agreed by Iran, the US, China, Russia, Britain, France and Germany – offered Tehran sanctions relief in exchange for curbs on its nuclear programme. But the US withdrew from the agreement in 2018, reimposing biting sanctions and prompting Tehran to begin rolling back on its commitments. Talk to salvage the nuclear deal began in late November, after being suspended when Iran elected a new ultraconservative government in June. Mr Wang told his Iranian counterpart on Friday that China believes the US is to blame for the current state of the deal, the foreign ministry said.