The European Union and NATO deplored Tuesday's deadly protests in Kiev, where at least five people were killed and scores hurt in clashes between protesters and police.

EU foreign policy chief Catherine Ashton said she was "deeply worried about the grave new escalation", saying in a statement that she condemned "all use of violence, including against public or party buildings."

NATO chief Anders Fogh Rasmussen said he was "seriously concerned" and urged "all parties to refrain from violence and to urgently resume dialogue, including through the parliamentary process."

The EU's enlargement commissioner Stefan Fuele, who with Ashton has been heavily involved in trying to defuse the Ukraine crisis, said the country's acting premier Sergei Arbuzov had told him the government would do all it could to keep the weapons on the street "silent".

"I was just on the phone with ... Arbuzov telling him that seeing in the streets Berkut, the special police, with Kalashnikov is a source of great concern," Fuele told journalists in Brussels.

"He assured me that he and the government would do what they can to make sure that those weapons stay silent. For the sake of Ukraine and its future I will pray that he is right."

In her statement, Ashton called for an urgent return to a parliamentary process.

"Political leaders must now assume their shared responsibility to rebuild trust and create the conditions for an effective solution to the political crisis," she said.

"A solution should include the formation of a new inclusive government, progress on constitutional reform and the preparation for transparent and democratic presidential elections. The EU stands ready to assist Ukraine in this process."