Russian President Vladimir Putin called US President Barack Obama on Friday to discuss a US diplomatic proposal for Ukraine and Obama told him that Russia must pull back its troops and not move deeper into Ukraine, the White House said.

It was believed to have been the first direct conversation between Obama and Putin since the United States and its European allies began imposing sanctions on Putin's inner circle and threatened to penalize key sectors of Russia's economy.

Russia's reinforcement of troops near Ukraine has brought the total forces there to as many as 40,000, US officials estimated on Friday in a build up that has increasingly worried Washington in recent days.

The White House noted specifically that it was Putin who called Obama, who is ending a four-nation trip in Saudi Arabia and had just returned to his Riyadh hotel after talks with King Abdullah.

Putin called to discuss a US proposal for a diplomatic resolution to the Ukraine crisis, which Secretary of State John Kerry again presented to Russian Foreign Minister Sergei Lavrov at a meeting at The Hague earlier this week.


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