The political crisis in Ukraine over the disputed presidential election appears to be deepening.
Yushchenko supporters are on the streets again
A meeting in the east of the country - power base of Prime Minister Viktor Yanukovych - is to discuss autonomy.
Mr Yanukovych's rival for the presidency, opposition leader Viktor Yushchenko, says this threatens the future of Ukraine.
Outgoing President Leonid Kuchma has urged both sides of the dispute to work towards a compromise.
The Russian government has suggested it might reverse its opposition to a new election. The European Union has already called for a new vote.
Ukraine's supreme court is due to meet on Monday to consider the validity of last Sunday's run-off poll, which saw pro-Russian Mr Yanukovych declared the winner.
Pro-Western Mr Yushchenko has claimed victory in the election, alleging massive fraud. His concerns have been backed by international observers.
The party of Mr Yanukovych says the meeting, in the eastern city of Severodonetsk, brings together 17 out of 25 regions, and will consider a proposal to create their own separate financial and economic structures.
Mr Yanukovych told delegates the disputed presidential election had pushed Ukraine to the "brink of catastrophe".
He said: "There is one step to the edge. When the first drop of blood is spilled, we will not be able to stop it."
Tens of thousands of protesting supporters of pro-Western Mr Yushchenko remain on the streets of the capital, Kiev.
POLITICAL CRISIS TIMELINE
21 Nov: Viktor Yanukovych declared winner of run-off poll
Independent observers declare the elections flawed, and thousands take to the streets
25 Nov: Supreme court suspends publication of result until it considers the opposition's complaints
26 Nov: Mr Yanukovych and Mr Yushchenko hold talks and agree to seek peaceful solution
27 Nov: MPs declare election invalid, pass vote of no-confidence in the election commission
Addressing them, Mr Yushchenko said the Severodonetsk meeting "could take a decision which would threaten the country's territorial integrity".
"Those people who will raise the issue of separatism will be held criminally responsible under the Ukrainian constitution," he said.
President Kuchma said working group talks between representatives of the
two rivals, designed to end the crisis, were going badly.
In a televised statement on Sunday, he accused Mr Yushchenko of not showing "goodwill", calling on him to lift a blockade by his supporters of government offices.
"No-one can say what sort of compromise can be found or whether one will be found at all," said Mr Kuchma.
The working groups were set up following talks on Friday with EU and Russian mediators.
According to the official election result, Mr Yanukovych won with 49.46% of the vote against Mr Yushchenko's 46.61%.
The supreme court suspended the presidential poll result on Thursday to consider the opposition's complaints.
In a non-binding resolution on Saturday, Ukraine's parliament declared the poll invalid, saying the result was "at odds with the will of the people".