The US has warned Russia it will face further sanctions if pro-Russia militia in eastern Ukraine do not disarm, as the Kremlin admits reinforcement troops have been sent to the border.
Barack Obama said the US could take further economic and diplomatic action against Moscow if an international agreement to calm tensions in Ukraine is not implemented.
Russia, Ukraine, the US and the European Union agreed on Thursday to a series of steps to "de-escalate" the crisis in Ukraine.
But many of the groups that took over government buildings in a bid to declare independence in eastern Ukraine have yet to leave, saying they will only do so if Ukraine's government steps down too.
US Secretary of State John Kerry told Russian foreign secretary Sergei Lavrov late on Friday that the "the next few days would be a pivotal period".
The EU has also indicated it will meet to discuss further sanctions if Russia does not act to make the militias disarm.
But earlier, the Kremlin had indicated Russia was not going to be bossed around, issuing a veiled threat.
Kremlin spokesman Dmitry Peskov told Russian television: "Our Western colleagues are trying to push responsibility towards our side. But it must be underlined: it is a collective responsibility."
"We have troops in different regions, and there are troops close to the Ukrainian border.
"Some are based there, others have been sent as reinforcements due to the situation in Ukraine," he added.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov Despite the deteriorating of relations, Russian president Vladimir Putin said on Saturday that he welcomed the appointment of the new Nato head Jens Stoltenberg.
He added that there was "nothing that would hinder a normalisation and normal cooperation" with the West.
In a further sign Moscow is determined not to retreat from its position, Putin said he would award medals to Russians who served during the seizure of Crimea.
In a televised Q&A on Thursday, he admitted for the first time that Russian troops had taken part in the annexation of the peninsula.
The White House said it was watching Moscow to see if it adhered to what had been agreed in Geneva.
Pro-Russians are occupying public buildings in 10 eastern Ukrainian cities and have been told to leave in the next few days or face consequences.
Kiev had previously declared the separatists as terrorists and sent troops to remove them, but had been unable to.
The separatists want a referendum on union with Russia, similar to the one held in Crimea that ultimately led to its annexation by Russia.
Sky's Katie Stallard, in Donetsk, said there was no sign of anyone there acting on the deal reached in Geneva.
She added: "None of those at the talks directly represented those on the ground, particularly those occupying the buildings."
Meanwhile, Europe's Baltic states are in talks to set up their own Russian-language television channel in a bid to counter the deluge of propaganda aimed at their ethnic Russian populations by Moscow-backed media.
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