Moscow has said a draft UN Security Council resolution on Iran's nuclear programme appears not to match positions agreed within the council.
Iran says it is enriching uranium only to generate electricity
The council's five permanent members plus Germany are meeting in New York to discuss sanctions over Iran's failure to stop sensitive nuclear fuel work.
The new resolution has been drafted by the council's three EU members.
Russia's foreign minister said the draft did not seem to "match those tasks the six sides agreed on".
"Our goal is to eliminate the risks of sensitive technologies getting into the hands of Iran until [UN nuclear inspectors] clarify the issues of interest to them, while maintaining all possible channels of communication with Iran," Sergei Lavrov said on a visit to Siberia.
The question is whether Russia and China, who both have the power to veto resolutions, will go along with the sanctions being proposed, the BBC's Laura Trevelyan reports from the UN.
They have significant economic ties to Tehran and Russia is resisting any restrictions on its work to build a new nuclear reactor at Bushehr in Iran.
Bans and freezes
Iran says it has a right to enrich uranium and it is doing it to make electricity but the same process can also be used to make a nuclear bomb, our correspondent notes.
The Security Council told Iran to stop what it was doing by the end of August or face action.
France's ambassador to the UN, Jean-Marc de la Sabliere, explained what was in the draft resolution:
"All states shall prevent the sale and supply to Iran of items and technologies which could contribute to its nuclear and missile programme.
"It says also that persons engaged in this programme shall be banned from travel.
"Also that funds and assets of these people and entities involved in Iran's nuclear and ballistic missile programme shall be frozen."
Richard Grenell, spokesman for the US mission to the UN, said on Wednesday that the US hoped to make changes to the EU three's draft but he gave no details.