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 .
NEW : Russian attacks damage hospital , killing one man . Ukraine : 10 pro - Russia militants dead in fighting . Separatist official puts number at 10 , says they attacked government aircraft . CNN ca n't independently confirm the number .