Nuclear program of Iran
U.S. President Obama reportedly sent a letter dated 20 April 2010 to President Lula of Brazil, in which he outlined a proposal of fuel swap. While expressing skepticism that the Iranians would now be willing to accept such a deal, having provided "no credible explanation" for the previous deal's rejection, President Obama wrote "For us, Iran’s agreement to transfer 1,200 kg of Iran’s low enriched uranium (LEU) out of the country would build confidence and reduce regional tensions by substantially reducing Iran’s LEU stockpile." Turkish Prime Minister Recep Tayyip Erdogan received a similar letter. A senior U.S. official told the "Washington Post" that the letter was a response to Iran's desire to ship out its uranium piecemeal, rather than in a single batch, and that during "multiple conversations" U.S. officials made clear that Iran should also cease 20% enrichment; however, the official stated "there was no president-to-president letter laying out those broader concerns".
Iran's 2018 lawsuit at ICJ against the United States
US President Donald Trump pulled out of a 2015 accord between Iran and "major world powers" whereupon some of the sanctions against Iran were lifted in exchange for Tehran accepting some limitations on its nuclear program. The US government then announced "unilateral plans" to re-impose sanctions against Iran. The Iranian government believed that the United States’ decision on 8 May 2018, to re-impose nuclear sanctions on Iran was a violation of the United States' international obligations, "especially articles 4, 7, 8, 9, 10" of JCPOA and the Treaty of Amity. Consequently, Iran filed a lawsuit with the International Court of Justice on 16 July 2018.