Denis Pushilin of the self-appointed Donetsk People's Republic told reporters the insurgents do not recognize the Ukrainian government as legitimate.
Ukraine and Russia agreed Thursday in Geneva to take tentative steps toward calming tensions along their shared border after weeks of conflict since Ukraine's former leader fled to Russia in February and Russia annexed Crimea in March. The deal calls for disarming all paramilitary groups and the immediate return of all government buildings seized across the country.
But Pushilin, speaking at the insurgent-occupied regional headquarters in the eastern city of Donetsk, said Ukraine's new interim government in the capital, Kiev, is also occupying public buildings illegally.
"This is a reasonable agreement but everyone should vacate the buildings and that includes (Arseniy) Yatsenyuk and (Oleksandr) Turchynov," he said referring to the acting Ukrainian prime minister and president.
Ukraine has scheduled a presidential election for May 25, but Pushilin reiterated a call to hold a referendum on self-determination for the Donetsk region by May 11. Such a referendum in Crimea led to its annexation by Russia.
Ukraine has faced months of turmoil, first in Kiev by protesters angry that former President Viktor Yanukovych wanted closer ties with Russia instead of Europe, then in eastern Ukraine by pro-Russian supporters. Now many of the buildings in the east occupied by the tacitly Moscow-supported insurgents are in the hands of highly trained gunmen, a situation that has complicated authorities' plans to retake them.
Pushilin said the insurgents would not handover their weapons until the government halts efforts to reclaim the occupied buildings.
"As far disarmament goes, the Kiev junta has already begun violating its agreements since yesterday, by announcing that it will not pull its troops out of Slovyansk and Kramatorsk," Pushilin said, referring to two cities occupied by the insurgency.
Despite announcing a security operation with great fanfare, the government in Kiev has taken few practical measures to reclaim its buildings. Prime Minister Arseniy Yatsenyuk told parliament Friday the government has drafted a law to offer amnesty to all those willing to lay down their arms and leave the occupied government buildings.
Russia has declined to recognize the legitimacy of Ukraine's interim government but it has not said they should vacate their offices.
Kiev-based political analyst Vadim Karasyov said Ukraine's fledgling government does not have the resources to resolve the standoff in eastern Ukraine militarily, so it's going to have to negotiate with the pro-Russian protesters.
"(Kiev) should finally listen to the demands of those people," he said. "They don't even know what their demands are. Maybe they are reasonable. The government in Kiev is pretending that there are no problems in the east."
In Washington, President Barack Obama conveyed skepticism late Thursday about Russian promises to de-escalate the volatile situation in Ukraine, and said the United State and its allies were ready to impose more sanctions if Moscow doesn't make good on its commitments.
Meanwhile, former prime minister and presidential hopeful Yulia Tymoshenko arrived Friday in Donetsk in a bid to defuse the tensions and hear "the demands of Ukrainians who live in Donetsk."
"I'd like to listen to these demands by myself and find out how serious they are, so that one could find the necessary compromise between the east and the west that will allow us to unite the country," she told The Associated Press.
Asked whether she would visit the occupied buildings, Tymoshenko said she would talk to people "representing various groups who seized the buildings."
Russian Foreign Minister Sergey Lavrov on Thursday emphasized that the requirement to abandon occupied building applied to all parties — an apparent reference to the ultranationalist Right Sector, whose activists are occupying Kiev city hall and a Kiev cultural center.
Russia's Foreign Ministry had no immediate comment on Pushilin's statement. But pro-Russian Ukrainian presidential candidate Oleh Tsaryov, whose statements often echo Moscow's stance, was quoted Friday as saying that Right Sector activists should be the first to lay down their arms.
The barricade-lined space in front of the Donetsk regional administration building, a mustering point for pro-Russian supporters, was almost totally empty Friday despite the warm weather. Patriotic Soviet-era music blared over loudspeakers.
One man in the square, 56-year-old militia member Igor Samoilov, said he would not support pulling back from any seized buildings.
"Russia can play these games with the West, but we will not," said Samoilov.
Sitting nearby, 86-year-old Yuri Kovalchuk said Moscow needed to intervene directly to settle matters.
"Peace will only prevail when the Kremlin will bring in its troops. As it did in Crimea," he said.
Vasilyeva reported from Kiev. Yuras Karmanau in Donetsk and Laura Mills in Moscow also contributed to this report.
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