Several hurdles still need to be resolved in negotiations between the US and Iran.

The fate of Iran’s uranium stockpiles

President Donald Trump suggested last week that Iran agreed to ship its stockpile of highly enriched uranium to the US, a claim that was quickly rebuked by a senior Iranian official who said the demand was a “non-starter.”

Iran has about 400 kilograms of 60% enriched uranium. One proposal that has been floated involves unfreezing Iranian assets in exchange for Tehran turning over its stockpile.

Iran has asked for major sanctions relief and unfreezing of assets north of $20 billion, a source familiar with the negotiations told CNN.

Curbs on uranium enrichment

The length of any suspension to Iran’s enrichment program remains another point of contention. An Iranian official who spoke to CNN rejected Trump’s assertion that Tehran agreed to halt the program indefinitely, saying Iran “will never accept” being an “exception from international law.”

During previous talks, American negotiators proposed a 20-year pause on Iran’s enrichment of uranium, a source familiar with the discussions told CNN. Iran responded with a proposal for a five-year suspension, which the US has rejected, according to a US official.

Reopening the Strait of Hormuz

The world breathed a sigh of relief on Friday when Iran announced it would reopen the key shipping route, which has been effectively shuttered for almost two months.

But the reprieve was short-lived. Iran says it is reimposing strict limits on shipping in response to Trump saying a US blockade on Iranian ports will continue until a deal is reached. On Sunday, marine traffic data showed no tankers have crossed the strait.

CNN’s Mitchell McCluskey, Frederik Pleitgen, Alayna Treene and Kevin Liptak contributed reporting.