U.S. President Barack Obama on Wednesday promised to increase Russia’s isolation, as the United States and the European Union agreed to work together to prepare possible tougher economic sanctions in response to Russia’s behavior in Ukraine.

Speaking after a summit with top EU officials and quoted by Reuters, Obama declared that Russian President Vladimir Putin had miscalculated if he thought he could divide the West or count on its indifference over his annexation of Crimea.

“If Russia continues on its current course, however, the isolation will deepen, sanctions will increase and there will be more consequences for the Russian economy,” he told a joint news conference with European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso.

Obama also said NATO should step up its presence in new east European member states bordering on Russia and Ukraine to provide reassurance that the alliance’s mutual defense guarantee would protect them.

In response to EU pleas to expand U.S. gas exports to Europe to reduce reliance on Russian supplies, Obama said a new transatlantic trade deal under negotiation would make it easier to license such sales.

Russia is refusing to recognize the Kiev government chosen by parliament after the overthrow of former President Viktor Yanukovich on February 22. It sent 6,000 troops to invade the Crimean peninsula and later annexed the reigon after a controversial referendum vote and a de facto military takeover.

The United States and the EU responded to Russia’s actions by imposing personal sanctions against Russian and Crimean officials involved in the seizure of the peninsula.

On Monday, Russia was suspended from the G8 group of leading nations but was not concerned by the move, as Foreign Minister Sergei Lavrov said that being kicked out of G8 would be “no big deal.”

In fact, Putin has remained unfazed by EU and U.S. economic sanctions, and has responded by drafting his own sanctions on top American senators.