"We are shocked... And deplore in the strongest possible terms the use of force and violence," Barroso said, squarely laying responsibility "to de-escalate this crisis" on the Ukrainian authorities.
"We... Will continue following closely these developments, as well as assessing possible actions by the EU and consequences for our relations," the president of the European Commission told a news conference.
Asked to elaborate on potential retaliation, Barroso said it was "premature" to decide on a course of action which would need to be approved by all 28 member states.
Several people were reported killed by gunshot after a day of intense clashes between pro-EU protesters and security forces.
Today's deaths were the first fatalities in two months of massive protests in Kiev over President Viktor Yanukovych's sudden refusal to sign a political and economic association pact with the EU in November after pressure from Moscow.
As anger mounted across Europe -- with French President Francois Hollande voicing "concern" and Britain's Europe Minister David Lidington demanding that Yanukoych "match his commitment to democratic norms and values with action" -- diplomats said talks on Ukraine were likely in Brussels tomorrow.
