Ukraine's Central Election Commission has expressed fears it may be impossible to hold next weekend's presidential election in the country's restive east.
The commission said on May 17 that it could not prepare for the vote in the region because of threats and "illegal actions" by separatists who have overrun towns and cities.
It called on Kyiv to take immediate measures to ensure security.
The warning came as the authorities in Kyiv held a second round of "national unity" dialogue under a Western-backed plan to try to defuse the crisis.
The talks in Kharkiv included a wide range of Ukrainian politicians, including pro-Russians, but no separatist leaders were invited and no progress was reported.
Russia, meanwhile, questioned how an election taking place under the "thunder of guns" could possibly meet democratic norms.
At the Kharkiv meeting, Ukrainian Prime Minister Arseniy Yatsenyuk said his government will not negotiate with the "terrorists" until they lay down their arms.
He said his government was willing to give wide powers to regional administrations but will never allow the "dismemberment" of the country.
Some officials from eastern Ukraine criticized the government for not paying enough attention to the grievances of the regions.
Valeriy Holenko, the head of the Luhansk regional council, said the devolution of powers offered by the government was not enough, and called for an end to "antiterrorist operations" in the east.
Oleksandr Bandurka, a Communist Party lawmaker and police general from central Ukraine, said that these negotiations made no sense because "we're not talking to those who oppose us. We cannot ignore them."
Ukraine's first president, Leonid Kravchuk, who is chairing the talks, angrily reacted that "no one in the world talks to killers and terrorists."
Yatsenyuk ended the meeting by quoting Ukrainian poet Taras Shevchenko and telling the leaders from eastern Ukraine, "We are ready to embrace you and hope that you are too."
U.S. State Department spokeswoman Jen Psaki rejected the "illegal actions" of unelected pro-Russian separatists in eastern Ukraine who want the region to become part of Russia.
But she said the United States supported the efforts by "elected and legitimate representatives" meeting in Kharkiv "to discuss constitutional and nonviolent approaches" to resolving their differences.
The roundtable talks are part of an Organization for Security and Cooperation in Europe-proposed road map to calm tensions ahead of Ukraine's May 25 presidential election.
Based on reporting by AP and AFP