"If the Russian leadership thought the world would not care about Ukraine, they clearly miscalculated," US President Barack Obama said at a press conference after the summit.
"There is still a way for Russia to work with Ukraine," Obama added.
"We support Ukraine," and in case of further escalation, the EU and the US were ready to "intensify sanctions", said European Council President Herman Van Rompuy in the same conference.
Van Rompuy also said that sanctions are a positive incentive to seek a diplomatic solution.
While the President of European Commission Jose Manuel Barroso called the Ukraine crisis a "wake-up call" for the EU to become less dependent on energy coming from "difficult spots", indicating Russia.