U.S. President Barack Obama has made phone calls to European heads of state regarding Ukraine, while on his vacation in the U.S. state of Florida.
The White House says Mr. Obama spoke individually with British Prime Minister David Cameron, French President Francois Hollande, and Italian Prime Minister Matteo Renzi on Saturday and held a conference call with the presidents of Lithuania, Latvia, and Estonia. No details about the discussions were immediately available.
The White House has promised to issue details about the calls later in the day.
On Friday, the Pentagon estimated there are now about 20,000 Russian troops in Ukraine.
Rear Admiral John Kirby says Defense Secretary Chuck Hagel spoke with Ukrainian Defense Minister Ihor Tenyuh on Friday and discussed humanitarian assistance and disaster relief.
The State Department also confirmed Secretary of State John Kerry spoke Friday over the phone with his Russian counterpart, Sergei Lavrov, as the Obama administration moved to impose sanctions on Russia.
The White House said President Obama told his Russian counterpart, Vladimir Putin, Thursday that Moscow's actions in Ukraine violate that country's sovereignty.
It was the first known direct contact between the leaders since Russian military personnel appeared in the Ukrainian territory last Saturday.
A statement Thursday said Mr. Obama proposed several diplomatic solutions to the standoff, which it said address "the interests of Russia, the people of Ukraine and the international community."
Mr. Obama has signed an executive order authorizing sanctions on those found to have stolen assets of the Ukrainian people or to have violated Ukraine's territorial integrity. The order blocks the transfer from the United States of assets belonging to anyone found to have undermined democratic institutions in Ukraine. It includes visa restrictions, but does not name targeted individuals.
The president said a March 16 referendum decreed by pro-Russian Crimean lawmakers on the future of the peninsula violates international law and Ukraine's constitution. He said any discussion about Ukraine's future "must include the legitimate government of Ukraine."