Ukrainian President Petro Poroshenko says those behind deadly Kiev clashes that erupted after a vote on autonomy for separatist eastern regions deserved severe punishment, calling the violence a "stab in the back."
"It was an anti-Ukrainian act for which all of its organisers without exception - all representatives of political forces - should be severely punished," he said in a televised address.
A 24-year-old member of the National Guard was killed and more than a hundred injured on Monday in street battles between the security forces and protesters outside the Vekhovna Rada parliament in Kiev.
The clashes erupted shortly after Ukrainian lawmakers gave their initial backing to deeply controversial legislation granting more autonomy to pro-Kremlin rebel-held regions in the east.
City authorities said two journalists were also hurt.
EU foreign affairs head Federica Mogherini expressed concern over the violence.
"Today's events are very worrying," she said in a statement.
"We offer our condolences to the family of the deceased law enforcement officer and our deepest sympathy to those injured in the explosion during the demonstration in front of the Verkhovna Rada."
OSCE Representative on Freedom of the Media Dunja Mijatovic also expressed concern over the violence and called for a "swift investigation into the case."
Russian President Vladimir Putin's spokesman said Moscow was also concerned at the clashes but quickly added this was Ukraine's domestic business.
"Of course, we condemn these manifestations of violence, we absolutely do not accept them," spokesman Dmitry Peskov told reporters.
It was the worst unrest in the Ukrainian capital since a popular uprising - that ended in bloodshed - ousted Moscow-backed president Viktor Yanukovych early last year, an event that set in train the separatist insurgency in Ukraine's industrial east.