The Kremlin insists an alleged US agent was not a high-level official and had been fired years ago.Read more
The foreign ministers of Germany and Russia have said they are working to preserve the Iran nuclear deal.
US President Donald Trump announced on Wednesday that the US would ditch the deal and reimpose sanctions.
German Foreign Minister Heiko Maas (pictured) said it was crucial Iran sticks to its obligations under the international 2015 deal despite the sanctions.
"It is necessary that Iran stays in the agreement. It is in Iran's interest, too, to keep the agreement alive," Mr Maas said after meeting Russian counterpart Sergei Lavrov in Moscow.
Mr Lavrov said it was crucial that any new US sanctions on Iran did not scuttle the deal.
Russia's foreign minister says the only evidence of a chemical attack came from the media.