(BRUSSELS) - The head of the European Union executive, Jose Manuel Barroso, warned Ukraine of "possible" reprisals after the deaths of pro-EU protesters Wednesday but stopped short of announcing sanctions.

"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.

The United States announced it had revoked the visas of several Ukrainian nationals linked to violence against protesters late last year, and said it was considering "further action" over the current clashes.

Several people were reported killed by gunshot after a day of intense clashes between pro-EU protesters and security forces.

Wednesday'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 on Thursday.

The EU for years has reached out to former Soviet satellites under its Eastern Partnership policy, which includes billions of euros in projects and grants, And one EU source suggested a means of action would be to trim or freeze such funds to Ukraine.

'We should not rule out targeted sanctions'

"There could be consequences for our relations with Ukraine, such as member states suspending negotiations on the association pact or deciding to impose sanctions if the situation worsens," said an EU official speaking on condition of anonymity.

In Lithuania, which with Sweden played a leading role in efforts to seal the pact with Ukraine that is at the root of the protests, Foreign Minister Linas Linkevicius told AFP that he favoured targeted sanctions such as those decided in Washington.

"Calls for dialogue and calls to stop violence do not work. Time is running out," he told AFP in the capital, Vilnius. "Our position has to be more firm."

"We should not rule out targeted sanctions" such as visa restrictions against "those officials who are responsible for the situation," he added.

Targeted EU sanctions are in place against several officials in Belarus, one of six nations involved in the EU's Eastern Partnership scheme.

Swedish Foreign Minister Carl Bildt also raised the idea of sanctions at talks with his EU counterparts in Brussels earlier this week.

"But no one has put forward a concrete proposal so far," said an EU diplomat who asked not to be named, and the next such ministerial meeting is set for February 10.

The EU official in charge of ties with Ukraine, Enlargement Commissioner Stefan Fuele, is to visit Ukraine on Friday and Saturday to discuss recent developments, his office said.

He will meet representatives of the authorities and opposition, as well as representatives of civil society.

Earlier, EU foreign policy chief Catherine Ashton also called for "an immediate end" to the violence, saying "those responsible will have to be held to account".

Joining the chorus of protests, NATO Secretary General Anders Fogh Rasmussen condemned developments in Ukraine, saying "violence can never be the answer to a political crisis".