Obama urges Putin to use influence to bring Ukraine back from brink
The two spoke for the first time in more than two weeks but showed little sign of agreement, with the US president calling on pro-Russian forces to de-escalate the situation, and Mr Putin denying that Moscow was interfering in the region.
The White House said Russia initiated the phone call, which came as pro-Russian forces deepened their insurgency in Ukraine's east, seizing more than a dozen government buildings.
The White House said: "The president expressed grave concern about Russian government support for the actions of armed pro-Russian separatists who threaten to undermine and destabilise the government of Ukraine.
"The president emphasised that all irregular forces in the country need to lay down their arms, and he urged president Putin to use his influence with these armed pro-Russian groups to convince them to depart the buildings they have seized."
The Kremlin said Mr Putin told Mr Obama that reports of Russian interference in the region were "based on unreliable information". The Russian leader also urged Mr Obama to discourage the Ukrainian government from using force against those protesters.
Both sides suggest that plans will go forward for talks on Thursday in Geneva between the US, Russia, Ukraine and Europe. But the White House said Mr Obama told Mr Putin that while a diplomatic solution remained his preferred option, "it cannot succeed in an environment of Russian military intimidation on Ukraine's borders, armed provocation within Ukraine, and escalatory rhetoric by Kremlin officials".
US officials say there is compelling evidence that Russia is fomenting the unrest in eastern Ukraine, but have suggested Mr Obama has not yet concluded that Mr Putin's actions warrant broader sanctions on key Russian economic sectors.
White House spokesman Jay Carney said: "We are actively evaluating what is happening in eastern Ukraine, what actions Russia has taken, what transgressions they've engaged in. And we are working with our partners and assessing for ourselves what response we may choose."
Administration officials confirmed yesterday that CIA chief John Brennan visited the Ukrainian capital of Kiev over the weekend, breaking with the administration's typical practice of not disclosing the director's travel. Ousted Ukrainian president Viktor Yanukovych accused Mr Brennan of being behind Ukraine's decision to send troops into the east to try to quash an increasingly brazen pro-Russian insurgency.
While US officials denied those accusations, confirmation of Mr Brennan's visit could provide fodder for Russian officials to create a pretext for further incursions into eastern Ukraine.
The two presidents last spoke on March 28. Since then, pro-Russian forces have stormed local government offices, police stations and a small airport in eastern Ukraine. The Ukrainian government has proved powerless to rein in the separatists, who are demanding more autonomy from the central government in Kiev and closer ties to Russia.
The White House has blamed the unrest on Moscow, saying there are similarities between the situation in eastern Ukraine and the Kremlin's manoeuvres in Crimea, the Black Sea peninsula Russia annexed from Ukraine last month.