Obama: Russia must pull back troops

US President Barack Obama has urged Russia to stop "intimidating" Ukraine and reduce the number of troops it has on its border.

He also called on Russia to "de-escalate the situation" and begin negotiations with Kiev.

Russia has massed a force of some 30,000 troops close to the eastern frontier of Ukraine in recent days.

Mr Obama told CBS News it may "be an effort to intimidate Ukraine, or it may be that [Russia has] additional plans."

In a separate development, ousted President Viktor Yanukovych has called for a national referendum to determine each region's "status within Ukraine".

He fled to Russia last month after massive demonstrations against him and clashes between protesters and police in which more than 100 people died. The Kremlin says the new government in Kiev came to power illegally.

President Obama, in the interview recorded before he left Italy on Thursday, said President Vladimir Putin had been "willing to show a deeply-held grievance about what he considers to be the loss of the Soviet Union".

But he warned that the Russian leader should not "revert back to the kinds of practices that were so prevalent during the Cold War".

"I think there's a strong sense of Russian nationalism and a sense that somehow the West has taken advantage of Russia in the past, " Mr Obama said. "What I have repeatedly said is that he may be entirely misreading the West. He's certainly misreading American foreign policy."

Mr Obama said the US has "no interest in circling Russia" and "no interest in Ukraine beyond letting Ukrainian people make their own decisions about their own lives."BBC