President Barack Obama's message to Russian President Vladimir Putin when traveling to Europe next week is to not "even think about messing around" with the Baltic states, the White House said Friday.

Obama is traveling to Europe next week for a meeting in Wales with other NATO leaders. He'll also make a stop in Estonia, where he will meet with the leaders of Estonia, Latvia, and Lithuania in an attempt to reassure allies amid burgeoning Russian aggression in Ukraine.

"The two stops are essentially part of the same effort to send a message to the Russians that their behavior is unacceptable," Charles Kupchan, the White House's senior director for European affairs, said in a conference call with reporters Friday afternoon.

"You have in Estonia a large Russian population, and therefore part of the message that the President will be sending is, we stand with you. Article 5 constitutes an ironclad guarantee of your security. Russia, don’t even think about messing around in Estonia or in any of the Baltic areas in the same way that you have been messing around in Ukraine."

NATO's Article 5 requires that all members of the alliance come to the defense of any member that is attacked or targeted.

Ukraine is not a member of NATO, and it has been one of Russia's goals to keep Ukraine from entering into both NATO and the European Union and thus forge closer ties with the West. Ukrainian Prime Minister Arseny Yatsenyuk said Friday the country would begin the process of seeking NATO membership.

When asked about Ukraine's possible future membership, Kupchan said it was not under discussion by NATO at this time but added that the "door is open" to any country that is "willing to contribute to security in the Euro-Atlantic space."

Ukraine said it would seek to become a member of NATO. NATO



Russia's neighbors like Estonia, Latvia, and Lithuania — which all have substantial Russian-speaking populations — have grown concerned in the face of increasing Russian intervention in Ukraine, which amplified this week.

Pro-Russian separatist rebels have opened a new front in the cities of Amvrosiivka and Starobeshevo, creating a fear is that Russia is attempting to create a land link between Russia and the strategic peninsula of Crimea. Russia annexed the peninsula special forces troops in March.

Ukrainian President Petro Poroshenko said Russian troops are leading a separatist counteroffensive in the east, bringing in tanks and firing artillery from inside Ukrainian territory. NATO subsequently backed up his claims, saying more than 1,000 Russian troops had crossed the border and were fighting in Ukraine.

"I think what you’ll see is progress on the defense spending side, progress particularly on increasing the readiness times of NATO forces," Kupchan said.

"Because I think one of the things that we’ve learned from the situation in Ukraine is that oftentimes in this new world that we live in, NATO or individual countries may be facing not armored columns coming across their border, which you can usually see in advance, but guys coming across in masks, you don’t know who they are — what we could call hybrid warfare, or asymmetric warfare. And that requires a very different kind of military response than NATO has traditionally been focused on."