Both Obama and Putin has emphasized the importance of an "immediate and sustained ceasefire" in east Ukraine, but at the same time noted that "significant differences" remained between the two countries, a Kremlin statement said.

The White House has also released a statement following the phone call, in which it said that President Obama has expressed “deep concerns” to President Putin about Russia's “increased support for separatists in eastern Ukraine.”

"[Barack Obama] reinforced his preference for a diplomatic solution to the crisis in Ukraine," a White House statement on the conversation said.

The two leaders agreed to keep open their channels of communication.

The Friday phone conversation, initiated by American side, has been the first personal contact of the two leaders since mid-July. The last spoke on July, 17, the day when Malaysian MH17 flight crashed over eastern Ukraine.

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