KYIV (Reuters) - An air strike hit a building sheltering civilians in Ukraine's embattled eastern city of Lysychansk on Thursday, killing at least four and wounding seven, local governor Serhiy Gaidai said.

       "The rescue operation is still ongoing," Gaidai wrote on the Telegram app on Thursday evening.

       The governor said a separate air strike on Thursday had hit a sanatorium building in Lysychansk and collapsed it, possibly causing further casualties.

       "It is likely that there are people trapped under the rubble," he said of the second strike, adding that a rescue effort was also underway there.

       Reuters could not independently verify the air strikes.

       Lysychansk sits just the other side of the Siverskyi Donets river to the battleground city of Sievierodonetsk, which over the last several weeks has seen some of the most brutal street fighting observed during Russia's invasion of Ukraine.

       (Reporting by Max Hunder; Editing by Frank Jack Daniel and Gareth Jones)