SEOUL - President Obama said today he believes President Vladimir Putin is "not a stupid man" but that tougher western sanctions on Russia would do little to change its course in Ukraine.

"There's going to come a point when he's going to have to make a fundamental decision," Obama said at South Korea's Blue House. "Is he willing to see an economy already faltered weaken further … or is he going to use military force and the kind of destabilizing activities that we see so far?

"That's the choice he's going to have to make," Obama said, "but we shouldn't make the choice easy for him."

Obama has said that a new package of economic sanctions is "teed up and ready to go" and could be deployed in a "matter of days, not weeks." But the White House has signaled that "technical issues" with their practical implementation and coordination with European allies still need to be resolved.

"The violations of sovereignty and territorial integrity in Ukraine is a principle that the U.S. has to stand up to," Obama said.

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At the same time, when asked whether he thinks new sanctions will make any difference, Obama bluntly acknowledged there are "no guarantees" and even suggested Putin was unlikely to abide.

"Mr. Putin, in my second term, has had an increasing tendency to view the world through a Cold War prism and to see Russia's interests as invariably in conflict with the West," he said. "I disagree with him with what's in Russia's interest, but he's the president of that country."

As for Putin's recent comment that he thinks Obama would save him if he were found to be drowning, Obama said he would save Putin.

"I absolutely would save Mr. Putin if he were drowning," the president said. " I would like to think that if anyone is out there drowning, I will save them. I used to be a pretty good swimmer - I grew up in Hawaii -though [I'm] a little out of practice."

(Song Kyung-Seok/Getty Images)