In an interview with CBS News, Obama said the world is unified in opposing and condemning what he called Russia's illegal occupation of Ukraine's Crimea peninsula. That occupation started last month.
Pentagon correspondent David Martin is reporting the Russians are massing another 40,000 to 50,000 troops on the Ukrainian border, with all they need for combat operations. In Friday's interview, Obama sent a message to Russia.
PRESIDENT BARACK OBAMA: It may be you've seen a range of troops massing along that border under the guise of military exercises, but these are not what Russia would normally be doing. It may simply be an effort to intimidate Ukraine, or it may be that they've got additional plans.
And in either case, what we need right now to resolve and de-escalate the situation would be for Russia to move back those troops and to begin negotiations directly with the Ukrainian government, as well as the international community.
SCOTT PELLEY: What is Vladimir Putin after?
PRESIDENT BARACK OBAMA: If you take him at his word, then --
PELLEY: Can you?
OBAMA: Well, on this I think he's been willing to show a deeply held grievance about what he considers to be the loss of the Soviet Union. ... 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, and that he wants to, in some fashion, reverse that or make up for that.
After the interview, Obama flew to Saudi Arabia for talks on the catastrophic Syrian civil war. In Syria, two branches of Islam are at war. Iran supports the Shia Muslim government. Saudi Arabia supports the Sunni Muslim rebels.
Saudi King Abdullah believes Obama has not done nearly enough for the rebel cause. Nearly 150,000 people have been killed, and more than two million are refugees.
OBAMA: To look at a country like Syria and see how it's been torn apart, to see the humanitarian crisis that's taking place, surely that is not consistent with any reasonable interpretation of what Islam is all about. To see children starving or murdered, to see families having to abandon their homes, you know, that's contrary to, I think, any religious doctrine that sensible people would embrace.
PELLEY: When you see those children starving and dying, as you put it, do you regret not applying U.S. force and not applying it early?
OBAMA: It is, I think, a false notion that somehow we were in a position to, through a few selective strikes, prevent the kind of hardship that we've seen in Syria.
PELLEY: And Syria's not worth that to you?
OBAMA: Well, it's not that it's not worth it. It's that, after a decade of war, you know, the United States has limits. And our troops who've been on these rotations and their families and the costs and the capacity to actually shape, in a sustained way, an outcome that was viable without us having a further commitment of perhaps another decade, you know, those are things that the United States would have a hard time executing. And it's not clear whether the outcome in fact would have turned out significantly better.
The White House tells CBS News Russian President Vladimir Putin phoned after President Obama landed in Saudi Arabia. The two leaders talked for an hour. The call is described as frank and direct and apparently centered on Russia opening negotiations directly with Ukraine.