Vitaliy Klitschko, the leader of the Ukrainian opposition party UDAR, has declared his pullout of the negotiations with the authorities on settling the ongoing political crisis, Ukrainian National Security and Defense Council Secretary Andriy Kliuyev said.

"The conversation failed to be constructive, and Klitschko started declaring his withdrawal from the negotiating process," Kliuyev said at a news conference on Tuesday.

He urged Klitschko to come back to the negotiating table, calling the opposition leaders' position "unwise" and suggesting that true policymakers should seek to settle the situation.

Kliuyev also urged the opposition to call on their supporters to renounce violence against police on Hrushevsky Street. "While some opposition leaders have disassociated themselves from what is happening on the street, I would ask them to urge their representatives to stop the violence," he said.

A meeting of a working group for settling the political crisis hosted by Kliuyev, in which Klitschko originally participated, took place at the presidential office earlier on Tuesday.

President Viktor Yanukovych did not attend the meeting. The presidential press service said he was in a conference with Prime Minister Mykola Azarov and First Deputy Prime Minister Serhiy Arbuzov to address Ukraine's socioeconomic development in 2014.

Klitschko told reporters he had come to the presidential office with the determination to meet with Yanukovych and hear the president "demand stopping the escalation of violence and starting to make steps toward settling the acute political crisis."