DONETSK, Ukraine - Pro-Russian separatists in eastern Ukraine vowed Thursday to press ahead with a referendum on independence, defying Russian President Vladimir Putin's surprise call for Sunday's vote to be postponed.
Having captured government buildings across eastern Ukraine and denounced the interim government in Kiev as fascists, the leaders of the "Donetsk People's Republic" argued that they would lose credibility if they canceled the vote.
"Civil war has already begun," Denis Pushilin, a prominent leader of the group, told a packed news conference in Donetsk. "The referendum can put a stop to it and start a political process."
The decision to proceed with the vote could be seen as a rebuff to Putin, whose call Wednesday for a postponement struck a more conciliatory tone than his previous statements on Ukraine.
It remained unclear what a referendum might look like, who would participate, how fair it might be, or even in how many or which cities it would be held.
But the separatists clearly felt they had little choice but to press on: Canceling the vote would leave them without even a fig leaf of popular legitimacy and deflate their movement, perhaps fatally.
Ukraine's acting prime minister, Arseniy Yatsenyuk, said Thursday that any referendum would lack legitimacy. Ukraine has said questions about the country's future should be decided in nationwide presidential elections scheduled for May 25, not in any regional vote.
Feeding a sense that the letup in tensions had been fleeting, Putin on Thursday led major military exercises that simulated a response to a massive attack on Russian soil, defense officials in Moscow said.
Kremlin-backed television showed vast salvos being fired across Russia, including intercontinental ballistic missiles from submarines, cruise missiles from a Tupolev bomber and scores of Grad rockets raining down on a practice range.
Putin said the strikes were part of exercises that were planned in November to demonstrate the high readiness of the country's "strategic offensive and defensive forces."
The separatists called the referendum to decide whether the Donbas region of eastern Ukraine, the nation's industrial heartland of Donetsk and Luhansk, should declare independence.
But with little coordination or trust among separatist leaders in different cities across the region, it was far from clear what a putative new republic would look like.
There was also widespread skepticism about the separatists' ability to stage a referendum with even a minimum of credibility.
Boris Litvinov, a leader of the referendum effort, said that about 3 million ballots have already been printed and 2.7 million of them distributed. The ballots ask voters whether they support the "independence of the Donetsk People's Republic."
But he said authorities in Kiev have denied the separatists access to voter rolls. Therefore, he said, the referendum would be an "open process" in which people would simply turn up at polling centers, show their passports, sign their names and cast their ballots.
After two days of mixed messages from Russia, Putin's real intentions about the referendum remained hard to read. Analysts in Moscow said he could be playing a double game, disassociating Russia from what is likely to be a deeply flawed contest while maintaining flexibility in how to respond.
Complicating the West's efforts to isolate Russia, the Kremlin announced Thursday that Vladimir Putin will join President Obama and European leaders in France next month for a ceremony marking the 70th anniversary of the D-Day invasion that hastened the end of World War II.
The June 6 commemoration would mark the first time Putin and Western leaders have come face-to-face since the outbreak of the crisis in Ukraine. The United States and Europe have condemned Russia's provocations, ordering sanctions on Putin's inner circle and cutting Russia's ties to some international organizations.
Still, leaders from Germany and France publicly welcomed Putin's decision to attend the observance at Normandy, raising questions about the effectiveness of recent efforts to ostracize the Russian president over Ukraine.
And while the White House said Obama would not meet one-on-one with Putin, U.S. officials did not appear to be seeking to stop him from attending.
"We would not expect France to disinvite Russia from this historic event commemorating World War II because of what's taking place in Ukraine," White House spokeswoman Caitlin Hayden said. "The events in Normandy on June 6 are focused on remembering the sacrifices of all our World War II veterans."