Russian President Vladimir Putin's goal is to impose "full control" over Ukraine, though not necessarily through military force, European Commission head Jose Manuel Barroso says.
Kiev and Western governments accuse Putin of remotely fomenting a pro-Russian insurrection in eastern Ukraine, and Barroso said Moscow's intervention in the country represented a dangerous precedent that flouted international law.
"I have no doubts that the goal of Mr Putin is to have full control of Ukraine," Barroso said at an event organised by the Atlantic Council think tank in Washington.
"I'm not saying that his goal is necessarily to occupy all Ukraine, but to have full control of Ukraine, that's his goal, I have absolutely no doubt.
"In fact, he said it to me; he said several times that an independent Ukraine was an artificial creation of the West," he said.
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Putin has long planned for Ukraine to be part of a Russian-led customs union and could not tolerate Kiev agreeing to a deal with the European Union, according to Barroso.
"The problem is that intellectually and emotionally, the leadership in Russia, and certainly president Putin, have not accepted the independence of Ukraine.
"They believe Ukraine should be part of Russia."
Sanctions adopted by the United States and the European Union are designed to show Russian leaders that there will be "serious consequences" for their actions in Ukraine, he said.
When it comes to sanctions, some critics say the EU has avoided tough measures against Russia, but Barroso said the European Union is doing "a lot".
He also said that the EU's response carried more weight than US sanctions because of the union's close trade links with Russia.
"Whatever we do, it will have a greater impact than what the United States can do, for an important reason: we are Russia's first trading partner, " he said.
Russia, which accounts for about a quarter of all EU gas supplies, has threatened to cut gas supplies to Ukraine, raising concerns among European states that rely on gas deliveries via Ukraine.
However, Barroso said Russia was also dependent on the European market because it paid its big bills on time.
