"We believe that no alternative exists so far," President Vladimir Putin's spokesman Dmitry Peskov told reporters, adding that Iran's position on the subject was paramount.

"We are in favour of keeping the Joint Comprehensive Plan of Action in its current form," Peskov added, referring to the nuclear deal hammered out in 2015.

He said the agreement was the product of the efforts of many countries.

"The question is, will it be possible to repeat such successful work in the current situation," Peskov added.

Iran's President Hassan Rouhani rejected the US and French calls, and the EU also insisted the current agreement must stay.

Trump faces a May 12 deadline to decide on the fate of the Iran nuclear accord and is demanding changes that European capitals believe would represent a legal breach.