"If there was ever any doubt, that Russia is responsible for the violence in eastern Ukraine. The violence is encouraged by Russia. The separatists are trained by Russia. They are armed by Russia. They are funded by Russia," Obama said.
The President, who earlier spoke with German Chancellor Angela Merkel, said he and Merkel agreed on the Russian role in Ukraine.
"Russia has deliberately and repeatedly violated the sovereignty and territorial integrity of Ukraine," he said.
"The new images of Russian forces inside Ukraine make that plain for the world to see. This comes as Ukrainian forces are making progress against the separatists," he said.
The President said the actions Russia had already taken and the major sanctions the US imposed with its European and international partners against it, Moscow was already "more isolated than at any time since the end of the Cold War,"
"Capital is fleeing. Investors are increasingly staying out. His economy is in decline. And this ongoing Russian incursion into Ukraine will only bring more costs and consequences for Russia," he said, adding that next week he will visit Europe to coordinate with closest allies and partners.
Obama, however, ruled out taking of any military action in Ukraine.
"We are not taking military action to solve the Ukrainian problem. What we're doing is to mobilise the international community to apply pressure on Russia. But I think it is very important to recognize that a military solution to this problem is not going to be forthcoming," he said.
"Now, the fact that Russia has taken these actions in violation of the sovereignty and territorial integrity of the Ukrainians has resulted in a weakening of Russia, not a strengthening of Russia. That may not be apparent immediately, but I think it will become increasingly apparent," he said.
What it's also done is isolated Russia from its trading partners, its commercial partners, international business in ways that I think are going to be very difficult to recover from, he said.
Noting that the US will continue to stand firm with its allies and partners, Obama said, what was happening was wrong and "there is a solution that allows Ukraine and Russia to live peacefully."
Ukraine is not a member of NATO, but a number of those states that are close by are.
"We take our Article 5 commitments to defend each other very seriously, and that includes the smallest NATO member, as well as the largest NATO member," he added.

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