Under the deal, Total (TOT) and China's CNPC agreed to invest billions of dollars in Iran to develop the giant South Pars gas field in partnership with Iran's Petropars.

It was the first investment of its kind since sanctions on Iran were relaxed in 2016 after Tehran promised to roll back its nuclear program. Trump has threatened to quit the nuclear deal if the U.S. Congress and America's allies fail to strengthen it.

"Either we can do the deal legally if there is a legal framework," Total CEO Patrick Pouyanné told CNNMoney Emerging Markets Editor John Defterios.

"If we cannot do that for legal reasons, because of [a] change of [the] regime of sanctions, then we have to revisit it."

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