Obama warns Putin of 'costs' for Russia on Ukraine

US President Barack Obama on Monday warned Vladimir Putin that Russia would face new sanctions if it failed to both stop the flow of weapons into Ukraine and halt support for separatists.

The White House said that Obama delivered the warning in a telephone call with the Russian leader, in which he called for "concrete actions" by Moscow to de-escalate the situation.

White House spokesman Josh Earnest said Obama used the call to drive home consistent US and Western warnings on Ukraine -- that Russia must stop supporting separatists in the east of the country and stop the flow of weapons across the border.

"Though we believe a diplomatic solution is still possible, Russia will face additional costs if we do not see concrete actions to de-escalate the situation," said Earnest.

The Kremlin said in its own statement about the call that Putin stressed the need for a true ceasefire in Ukraine and direct talks for the warring parties.

It was the first time that Putin and Obama had spoken since they met at D-Day 70th anniversary celebrations in Normandy, France on June 6.

State Department spokeswoman Marie Harf meanwhile said that Washington had new information that tanks were being readied at a site in southwestern Russia to be sent into eastern Ukraine.

Washington said last week that a number of Russian tanks and armored personnel carriers had already made the trip across the border.