NATO has released satellite photographs showing what it says are 40,000 Russian troops massed near the Ukraine border, along with tanks, aircraft and other hardware said to be awaiting orders from Moscow.
The imagery, released to news outlets Thursday, follows repeated Russian assurances that the deployment is no cause for international alarm.
That satellite intelligence comes as the government in Kyiv seeks to defuse tensions in eastern Ukraine, where pro-Russian protesters seized control of government buildings earlier this week and issued demands for a vote on joining the Russian Federation.
The White House says President Barack Obama conferred with German Chancellor Angela Merkel by phone Thursday, and that both leaders again called on Moscow to pull back its troops from the border regions.
Meanwhile, several surveys, including a poll released Wednesday, have found that residents of the key eastern Ukrainian city of Donetsk overwhelmingly oppose any move to join Russia.
That survey, conducted March 26-29 in conjunction with Donetsk National University, showed less than 27 percent of city residents supporting the building seizures, and only 4.7 percent wanting to separate from Ukraine.
A poll conducted by the Gallup organization in conjunction with the International Republican Institute found just 4 percent of respondents favoring secession. That survey was released April 5.
With secession support appearing minimal in the Russian-speaking east, Ukraine's acting president Oleksandr Turchynov promised amnesty for the demonstrators if they give up their weapons and abandon the government buildings under siege in Donetsk and Luhansk.
Mr. Turchynov said Thursday he is willing to make his promise official in a presidential proclamation.
In a related development, Russian President Vladimir Putin warned European leaders that the flow of Russian natural gas through Ukraine to the West could be interrupted if Kyiv fails to pay off its $2.2 billion gas debt to Moscow.
Mr. Putin also said the unpaid arrears will force Russian supplier Gazprom to demand that Ukraine pay for gas deliveries in advance.