He told reporters in Moscow that Iran is rolling back its obligations "without any violations of the Treaty on the Non-Proliferation of Nuclear Weapons."

The NPT, which came into force in 1970, calls on nations "to achieve the cessation of the nuclear arms race and to undertake measures in the direction of nuclear disarmament".

Iran has warned that leaving the non-proliferation treaty is one of the "many options" it has to retaliate against US sanctions.

President Hassan Rouhani said Tuesday that Iran would resume uranium enrichment at an underground plant south of the capital, taking another step back from another treaty -- Iran's troubled 2015 nuclear agreement with major powers.

The Kremlin has expressed concern about Tehran's announcement but also said Russia understood its concerns over the "unprecedented and illegal sanctions" against Iran.

On Wednesday, Moscow repeated this point, saying that European powers should do their part.

"They are demanding that Iran fulfil all (obligations) without exception but are not giving anything in return," Russia's top diplomat said.

Washington's abandonment of the 2015 deal in May last year, followed by its reimposition of crippling sanctions, prompted Tehran to begin a phased suspension of its own commitments this year.

Iran has repeatedly warned the remaining parties -- Britain, China, France, Germany and Russia -- that the agreement can only be rescued if they help it circumvent US sanctions.

The 2015 Iran nuclear deal with the six world powers had given the Islamic Republic sanctions relief in exchange for curbs on its nuclear program.