Donetsk, Ukraine (CNN) -- Conflicting accounts emerged Wednesday from heightened fighting in eastern Ukraine, with a Ukrainian government official claiming forces loyal to Kiev had inflicted heavy losses on separatists and a pro-Russia official boasting that militants had downed government jets and helicopters.
A Ukrainian government spokesman claimed that more than 300 pro-Russia militants had been killed and at least 500 wounded during an ongoing Ukrainian military operation in the towns of Krasny Liman and Slovyansk.
The self-declared separatist mayor of Slovyansk, however, said only 10 separatist fighters had died and 12 were injured in the fighting.
CNN could not immediately confirm either report.
But CNN's Tim Lister, reporting from Donetsk, Ukraine, questioned the government account, saying it would be "incredibly difficult" to confirm such a body count amid the heightened fighting.
"It would be a dramatic escalation on anything we've ever seen before," he said.
Ukrainian anti-terror spokesman Vladislav Seleznev said two Ukrainian soldiers also died and 45 were wounded in the fighting Tuesday night, part of an ongoing military operation meant to sweep pro-Russia militants from eastern Ukraine strongholds where the government claims they have been hiding in hospitals, medical clinics and recreational facilities.
On the separatist side, the self-declared mayor of Slovyansk, Vyacheslav Ponomarev, said pro-Russia fighters had shot down two Ukrainian jets and destroyed a tank and four armored personnel carriers in Tuesday's fighting. On Wednesday, militants shot down two Ukrainian helicopters, claimed.
While the casualty figures conflict, what is not in doubt is the dramatic uptick in violence in separatist-held areas of eastern Ukraine.
Video emerged Wednesday of damage to a hospital in Krasny Liman after it was hit by five rockets. The facility, which serves mainly railway workers, was hit Tuesday, according to Vladimir Seliyvanov, with Dontesk Railways. Four people, including a surgeon, were wounded in the attack, he added.
The images showed the impact of several detonations and many broken windows at the hospital.
It's not clear if the hospital was hit because militants were thought to be taking cover there or because of inaccurate targeting. Seliyvanov would not comment on whether injured separatists were being treated there.
At the nearby railway station, one man was killed in what appears to have been another rocket attack.
The official Donetsk Regional Authority says that clashes in Slovyansk continue. "Terrorists are trying to escape (the) encirclement together with civilians evacuating from the area. The Ukrainian military is taking measures to identify militants in order not to let them escape."
In Luhansk, the government said separatist fighters had taken over two military bases, one run by the Border Guard and the other by the National Guard.
Border Guard troops retreated from their base after it had been heavily damaged in 12 hours of fighting on Monday, the Border Guard Service said on its website. Separatists then moved in, the agency said.
The Ukrainian National Guard said troops at its base in Luhansk used up all their ammunition trying unsuccessfully to fight off an attack.
Video from a National Guard base in the city appeared to show its detachment surrendering to separatists early Wednesday.
The National Guard said three of its troops were inured and six attackers killed. The other troops at the base had been safely relocated, it said. CNN could not independently confirm the casualty figures.
The heightened fighting comes as U.S. President Barack Obama visits Ukrainian neighbor Poland. Obama met with Ukrainian President-elect Petro Poroshenko on Wednesday, when the U.S. leader vowed to stand with Ukraine in the face of Russian aggression.
"We will not accept Russia's occupation of Crimea or its violation of Ukraine's sovereignty," Obama said in Warsaw. "Our free nations will stand united so that further Russian provocations will only mean more isolation and costs for Russia."
Journalist Azad Safarov reported from Donetsk and journalist Victoria Butenko reported from Kiev. CNN's Michael Pearson wrote from Atlanta. CNN's Nick Paton Walsh, Laura Smith-Spark and Jim Acosta also contributed to this report.