US Secretary of State John Kerry has said Sergei Lavrov told him Vladimir Putin is not prepared to make any decision on Ukrainian's Crimea region until after Sunday's referendum.
Mr Kerry said the US and the EU are already clear on the referendum, describing it as "illegal under the Ukrainian constitution".
He said the international community will not recognise its outcome.
Mr Kerry said he also told Mr Lavrov, Russia's Foreign Minister, the US was concerned about the deployment of Russian troops in military exercises on the Ukraine border and the "increased anxiety" it had caused amid the current crisis.
John Kerry warned of "consequences" after his Russian counterpart made clear Moscow would respect the outcome of Crimea's referendum.
Foreign ministers meeting in Brussels will decide on Monday on sanctions for Russia if there is no de-escalation in Ukraine.
Crimea's new information minister has told ITV News that the planned referendum is no different to the situation in Scotland and Catalonia.