KYIV, July 3 (Reuters) - Ukraine's state energy company Naftogaz increased its domestic gas production and pumped more gas into underground storages to prepare for cold winter months amid a severe power crisis, its CEO said on Wednesday. CEO Oleskiy Chernyshov said that Ukraine had 9.5 billion cubic metres of natural gas in its underground storage as of July 3. Naftogaz raised its domestic gas production by 8% to 7.3 bcm in the first half of the year. "A very big challenge ahead of this winter is energy supply and generation of additional electricity volumes. We should count on additional volumes that could be generated with the natural gas," Chernyshov told Ukrainian TV. Since March, Russian missile and drone attacks knocked out about half of Ukraine's available generation capacity and forced rolling blackouts across the country despite lower levels of consumption in the summer. Ukraine's energy industry is rushing with repairs. Officials, cities and businesses also want to create more decentralized power generation, including by using gas turbines. Chernyshov said that Naftogaz was pumping gas into its underground storages quicker than last year despite war time challenges. The company already pumped 400 mcm of gas more this year compared with the same period of 2023 with total volumes reaching 9.5 bcm, he said. "This volume is enough to plan reaching more than 13 billion cubic metres in volumes at the start of the 2024-2025 heating season," Oleksiy Chernyshov told Ukrainian TV. (Reporting by Olena Harmash, Editing by Louise Heavens and Elaine Hardcastle)