Fears that Ukraine could split in two mounted on Saturday as regional lawmakers in the pro-Russian east questioned the authority of the national parliament.
Parliament sought to oust President Viktor Yanukovych and he left the capital, with protesters taking control.
After a tumultuous few days that are changing Ukraine's political destiny, Mr Yanukovych left Kiev for the city of Kharkiv, his support base in the country's Russian-speaking east. A presidential aide said he has no intention of abandoning power.
Attention shifted on Saturday from the sprawling Kiev protest camp to Kharkiv, where governors, provincial officials and legislators gathered.
Top Russian lawmakers joined the meeting, too, while thousands of angry protesters gathered outside, chanting "Ukraine is not Russia!"
Russia, the US and the European Union are deeply worried about the future of Ukraine, a nation of 46 million whose loyalties and economy are divided between Europe and long-time ruler Moscow.
The leaders gathered in Kharkiv approved a statement calling on regional authorities to take full responsibility for the constitutional order on their territory.
Some called for forming volunteer units to protect against force by protesters from western regions. The assembly urged army units to maintain neutrality and protect ammunition depots.
"The events of recent days in the capital Kiev have brought central authorities to paralysis and destabilised the situation of the government," lawmaker Vadim Kolesnichenko said at the congress, according to Russian news agencies.
He accused the opposition of not upholding its side of a breakthrough agreement on Friday with Mr Yanukovych to order protesters to give up weapons and abandon protest camps.
Mr Yanukovych is in Kharkiv to meet with voters and appear on local television, his aide said.
Also in Kharkiv is his main foe, jailed ex-prime minister Yulia Tymoshenko.
Ms Tymoshenko's arrest in 2011 and conviction on charges of abuse of office were widely seen as a case of political revenge.
After a European-mediated deal between the president and the opposition on Friday, the Ukrainian parliament voted to decriminalise the charge on which Tymoshenko was convicted.
A spokeswoman for Ms Tymoshenko, Natasha Lysova, told The Associated Press that a decision taken by parliament on Saturday means Ms Tymoshenko must be freed immediately. Earlier, Ms Lysova had said Ms Tymoshenko had already been freed.