Right Sector members protesting outside the parliament building in Kiev - 27 March 2014 Hundreds of Right Sector activists protested outside parliament in Kiev. Photo: BBC NEWS

Right Sector activists blocked the parliament (Rada) building in Kiev on Thursday night and smashed windows.

They blamed the interior minister for the killing of a Right Sector leader.

Meanwhile, ousted President Viktor Yanukovych has called for a national referendum to determine each region's "status within Ukraine".

He fled to Russia last month after massive demonstrations against him and clashes between protesters and police in which more than 100 people died. The Kremlin says the new government in Kiev came to power illegally.

"As a president who is with you with all my thoughts and soul, I urge every sensible citizen of Ukraine: Don't give in to impostors! Demand a referendum on the status of each region within Ukraine," said Mr Yanukovych, quoted by Itar-Tass news agency.

He denounced fresh presidential elections planned for 25 May.

The Right Sector played a key role in the Kiev clashes that led to the removal of Mr Yanukovych

At a parliament session on Friday his successor, Mr Turchynov, called the Right Sector rally outside parliament "an attempt to destabilise the situation in Ukraine, in the very heart of Ukraine - Kiev. That is precisely the task that the Russian Federation's political leadership is giving to its special services".

Right Sector activists are furious over the death of Oleksandr Muzychko, better known as Sashko Bily, one of their leaders. The interior ministry said he died on Monday night in a shoot-out with police in a cafe in Rivne in western Ukraine.

Right Sector played a prominent role in the Kiev protests - and the clashes with police - which led to the removal of Viktor Yanukovych from power. Its main support base is in western Ukraine.