The Ukrainian opposition has delayed a parliamentary session in which a new prime minister was due to be elected.
Yulia Tymoshenko patched up a rift with "Orange" allies
Former PM Yulia Tymoshenko - a key figure in the 2004 "Orange Revolution" - had been nominated and her election was expected to be a formality.
But opposition members have been staging a sit-in in parliament for several days to obstruct its business.
The pro-Russian MPs claim the governing coalition is violating the constitution by pushing for a non-secret ballot.
One of the coalition leaders - Socialist Party boss Oleksander Moroz - has said that all sides will meet on Friday to try to find a way out of the impasse.
The MPs say they will blockade the parliament for the next four weeks in an attempt to force a new election to be called.
The governing coalition is made up of the pro-Western parties that supported the mass protests of the Orange Revolution.
This is not the first time that Ukraine's parliament has faced a blockade, the BBC's Helen Fawkes reports from Kiev.
When it happened in the past, MPs held their session in another building in the capital.
It is thought this option is being considered.