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.
Vladimir Putin has dismissed Western claims that a Crimea referendum is illegal and confirmed the public vote on whether to the Ukrainian region should join Russia will go ahead on Sunday as planned.
The Russian President reiterated his country's stance in a telephone conversation with UN Secretary Ban Ki-moon.
The Kremlin said Mr Putin told Ban the referendum "fully corresponds to the norms of international law and the UN Charter".
Russian Foreign Secretary Sergei Lavrov has said the Ukrainian region of Crimea means more to Russians than the Falklands mean to British people.
He said the planned referendum in Crimea is in line with international law - a claim which US and EU leaders dispute - and argued that the region should be treated similarly to Kosovo, which was unilaterally declared independent from Serbia in 2008.
Mr Lavrov also flatly rejected reports which emerged today claiming that the Kremlin is planning to invade eastern Ukraine. He said Moscow has "no plans" to undertake such an operation.
Russia's Foreign Minister Sergei Lavrov has said US Secretary of State John Kerry made no mention of a threat of sanctions during the pair's private talks over the Ukraine crisis earlier today.
Mr Lavrov said he was aware of the reports of sanctions, which claim the US and EU are planning to freeze the assets and block the travel of up to 130 Russians if the Crimea referendum goes ahead on Sunday.
Mr Lavrov said such sanctions would be "counter-productive" and would not contribute to the countries' mutual interests.
Russia's Foreign Minister Sergei Lavrov has said differences remain with the West over the Ukraine crisis after private talks with US Secretary of State John Kerry.
Speaking at a news conference at the Russian Embassy in London, he said his country is deeply concerned that measures to ensure order in Ukraine are not being taken.
Mr Lavrov said Russia would continue to respect the will of the people in Crimea ahead of Sunday's controversial referendum and denied Moscow was acting aggressively in the region.
He added that no international structure is needed to mediate in Russia-Ukraine relations.
Russia's Foreign Minister Sergei Lavrov is holding a news conference at the Russian Embassy in London after private talks with US Secretary of State John Kerry over the Ukraine crisis.
Watch it live below:
The US Department of State and the Russian foreign ministry have posted pictures of John Kerry and Sergei Lavrov taking a stroll in the garden of the US Ambassador's residence in London:
Lavrov and Kerry. Hope they will be back http://t.co/ZXDFNSCzhE
Break is over. Match continues. http://t.co/C3Dmf4rq2D
The CEOs of Russia's two biggest companies are reportedly included on a list of over 100 Russians who could be hit by travel bans and asset freezes by the EU as punishment for the Kremlin's continuing military intervention in the Crimea region of Ukraine.
ITV News Europe Editor James Mates tweeted:
EU believed to have drawn up list of 120-130 Russian officials to be targeted with sanctions, incl heads of Gazprom + Rosneft #crimea
The preliminary list was compiled by European diplomats and runs to five pages, Reuters reported.
David Cameron and John Kerry enjoyed a bit of a natter earlier today as they posed with William Hague for the cameras to mark the US Secretary of State's visit to Downing Street before his crisis-talks with Russia's Sergei Lavrov.
After the traditional handshake welcome, the Prime Minister described having a "lovely time" in Israel's boisterous parliament, the Knesset, a few days ago.
Mr Kerry responded that he looked forward to Mr Cameron's "download" on the key visit before joking with Mr Hague about them regularly crossing paths.
The group ended the staged sit-down by reiterating their commitment to taking action against Russia if a diplomatic solution to the Ukraine crisis cannot be found.