The new Ukrainian government struck the separatists in this eastern province with a major military offensive on Monday, battling them over an important provincial airport in ground fighting that lasted for hours. The rebels were left scattered and shaken, just one day after a successful national election they had tried to disrupt.
The airport battle was the first time the Ukrainian military had moved so aggressively against the separatists, who took over government buildings in two eastern provinces in March, after weeks of low-grade military maneuvers meant to stop their spread to other areas.
There was no immediate indication that the Ukrainian military's operations extended any further than the strategically important airport and surrounding area. Experts said that while the military's attack might have put the separatists on the defensive, it was unlikely to stop their power.
As fighting lasted into a rainy evening, the military claimed to have evicted the separatists from the airport, and had cordoned off the area with roadblocks. But the sporadic sounds of weapons fire could still be heard, and it was not clear that government soldiers were in full control. The airport remained closed, and some local news outlets reported that it was burning.
"I don't see this ending anytime soon," said Oxana Shevel, a political science professor who specializes in Ukraine at Tufts University in Boston. "The Ukrainian government is saying, This is where we draw the line." Its ability to retake the airport, she said, "doesn't dramatically change things."
Even so, the routing of the rebels from the airport changed the optics of the situation here in favor of the Ukrainian military, which had suffered setbacks for weeks, and had been seen by many Ukrainians as ineffectual.
Fighter jets screamed and automatic gunfire popped for hours in and around the airport, with ground battles against separatists spilling outside its tall black gate. Thick black smoke dotted the sky and helicopters flew just above the trees, shaking small houses and blowing the grasses in their garden plots.
The rebel seizure of the airport early Monday suggested a new escalation by the militants who in recent days have appeared to lose the political support of the Kremlin, at least publicly. On Friday, President Vladimir V. Putin of Russia suggested that he would respect the results of Sunday's election, in which Petro O. Poroshenko, a Ukrainian billionaire who knows Mr. Putin, was elected in a landslide. Many here say separatist leaders had grown confident after months of swaggering across the provinces with virtually no pushback from central authorities.
The fractious groups are not directly under Mr. Putin's control, and the Kremlin has denied that its military is involved in the conflict here. But support can come in many forms, and it is far from clear that Mr. Putin has any intention of giving up what appears to be a useful geopolitical lever: violence and instability in Ukraine's east that has left the West flustered.
More from The New York Times:
"What Putin wants is for Ukraine to be weak," said Lucan A. Way, a political scientist at the University of Toronto who specializes in Ukraine and has lived in Donetsk. "Just because he gives verbal support for the new Ukrainian government does not mean that he will stop trying to foment unrest in the east."
By issuing statements of support, Mr. Putin "gets to look like a statesman," and blame whatever problems emerge on the new government, Professor Way said. "He has created a Frankenstein that he cannot control, and may not even want to," he said.
Many in Ukraine had feared that Mr. Putin sought the eastern regions themselves, and was putting troops in position to potentially seize them in the same way he did Crimea, the southern peninsula on the Black Sea that Russia annexed two months ago, setting off a major international confrontation.
But a subtler maneuver is now emerging, and many experts believe that the most desirable result for Mr. Putin would be for the troubled areas to devolve into breakaway status, similar to South Ossetia within Georgia and Transnistria within Moldova, a possibility that ordinary citizens are already talking about.
"It's a mess, it's anarchy," said Yevgeny Kaplenko, a retired welder, who stood near his small brick house and yard planted with roses near the airport, as gunfire popped. "This is going to be a second Transnistria. That's what awaits us."
That outcome would be considered poisonous by many Ukrainians, and would likely have far more serious repercussions for the world, given Ukraine's enormous size, severe economic problems and geopolitically strategic location in the heart of Europe.
"Putin doesn't want to take these regions and foot the bill for all these old industries," Professor Shevel said. "He would rather there be instability, which makes Ukraine less attractive to Europe and makes it easier to extract concessions from the government."
The day's events started shortly after 3 a.m., when dozens of armed men from the Donetsk People's Republic showed up at the airport and demanded that all Ukrainian military and security personnel leave, the airport's press service said. The Ukrainian military later issued an ultimatum for the men to leave and began to attack, shortly after 1 p.m., when they defied the eviction order. A military spokesman said the operation included fighter jets as well as several helicopters, which transported Ukrainian soldiers.
Pro-Russia militiamen took up positions behind trees close to the entrance, near a Metro supermarket. One of them, shot in the leg, was evacuated in a new Audi, its license plate obscured with tape. Fighters fired a rocket toward the airport, then retreated, under sniper fire, to an area where a friendly resident agreed to drive some of them in his blue car.
The rebels seemed shaken by the forcefulness of the military response. At the Donetsk government headquarters, nervous separatists briefed journalists.
"I am forced to appeal directly to Vladimir Vladimirovich Putin for any possible aid," said Denis Pushilin, the speaker of the self-proclaimed Donetsk People's Republic. When asked what kind of aid — military or economic — he said, "any."
Late Monday night, a Ukrainian military spokesman, Alexei Dmitrashkovsky, said by telephone that the army had established full control over the airport and that several of the militant leaders had requested safe passage, including one known by the nickname, Abver, described as a Russian passport holder. That claim could not be corroborated.
After midnight, Kalinin Hospital's deputy head doctor, Andrey Sokoleyvich, said the facility had received five people with shrapnel and bullet wounds. Late Monday evening, a social media account run by the rebels issued a call for doctors to come urgently to several city hospitals.
At the city's main trauma hospital, a woman wearing a flak jacket with a medical cross and carrying a holstered pistol said curtly that the wounded, who she claimed numbered fewer than 10, had been taken to other hospitals.
Earlier, as evening fell, a crowd of rebel sympathizers gathered outside the occupied government headquarters and some demanded that weapons be given to ordinary citizens, reflecting a growing siege mentality. Yaroslav Krakov, 33, said that every time he went to the rebels to demand a gun he was told none were left.
"We have no one else," he said. "Russia does not need us, that much is obvious. We are nothing to Kiev anymore. We only have Pushilin and ourselves."