Barroso, speaking during a debate in the European Parliament, called the Ukraine crisis "a test of our union." He said the outcome will determine the "geopolitical configuration" of Europe for many years.
"Our immediate goal and objective should be to de-escalate the situation and find a peaceful solution to the current crisis, in full respect of international law," he said. "Any attempt to legitimize a referendum in Crimea is contrary to the Ukrainian constitution and international law and quite clearly illegal."
Barroso said the EU is also increasing financial aid to Ukraine. The commission announced Tuesday that tariffs for most Ukrainian products are being eliminated temporarily.
Almost 95 percent of goods from Ukraine not be subject to customs duties through Nov. 1, the Ukrainian News Agency reported.