Supporters of Prime Minister Viktor Yanukovych in eastern Ukraine have announced they will hold a vote next Sunday for a semi-independent area.
Yushchenko supporters are on the streets again
The move by the Donetsk region council came as opposition supporters kept up the pressure to overturn the result of the disputed presidential poll.
Opposition leader Viktor Yushchenko earlier said those promoting autonomy should be held criminally responsible.
The supreme court is to consider fraud claims in the run-off poll on Monday.
The court has suspended the official results which saw pro-Russian Mr Yanukovych declared the winner of the presidential election, which took place a week ago.
Pro-Western Mr Yushchenko has declared himself the rightful winner, alleging massive vote-rigging. His concerns have been backed by international observers.
Outgoing President Leonid Kuchma has urged both sides to work to find 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.
The Donetsk regional council voted 164-1 to hold the referendum on 5 December on giving the region the status of a republic within Ukraine.
"We won't tolerate what's going on in Ukraine," Donetsk region governor Anatoly Bliznyuk told regional lawmakers.
"We have shown that we are a force to consider."
The Donetsk resolution came after Mr Yanukovych met about 3,500 local officials in the eastern city of Severodonetsk who voted for "a referendum to be held in December this year to determine the region's status".
He told delegates the disputed presidential election had pushed Ukraine to the "brink of catastrophe".
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
28 Nov: Eastern regions threaten to secede if Mr Yushchenko is declared president
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."
But Mr Yanukovych said he did not support the moves for a referendum in an area dominated by Russian speakers that have always looked more towards Moscow than Kiev.
Tens of thousands of opposition supporters have continued to hold protests in the capital, Kiev.
Addressing his supporters earlier, Mr Yushchenko said "those people who will raise the issue of separatism will be held criminally responsible under the Ukrainian constitution".
President Kuchma said talks between representatives of the two rivals, set up following talks on Friday with EU and Russian mediators, were going badly.
According to the official election result, Mr Yanukovych won with 49.46% of the vote against Mr Yushchenko's 46.61%.
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".