The United States and European Union are united in their determination to isolate Russia in connection with its military aggression against Ukraine.

U.S. President Barack Obama said this after the EU-U.S. summit in Brussels on Wednesday, Ukrinform reported.

"Europe's progress rests on basis principles, including respect for international law, as well as the sovereignty and territorial integrity of nations. That's what Russia violated with its military action against Ukraine. The United States and Europe stand united on this issue. We are united in our support for Ukraine and for the need to provide economic assistance to help stabilize its economy. We are united in our commitment to Europe's security. We are united in our determination to isolate Russia and impose costs for Russia's actions," the U.S. leader said.

He noted that Russia was currently left alone and that this was confirmed by the position of the states at the UN Security Council, G7 members, as well as the member states of the European Union and NATO.

Obama said that the Russian government had decided to annex Crimea after a referendum that no one outside Russia took seriously.

European Council President Herman Van Rompuy, in turn, said that in the event of further escalation of the conflict on the part of Russia Europeans and Americans were ready to step up sanctions.