WIESBADEN, Germany, March 2 (Reuters) - The United States is hosting war planning exercises in Germany for Ukrainian military officers to help them think through upcoming battlefield decisions, officials said on Thursday, ahead of the next phase of the year-old conflict with Russia. Ukrainian forces repelled Russia's advance on Kyiv early in 2022, and the conflict, which Moscow calls a "special military operation," has become one of grinding trench warfare in the east and south. Milley expressed optimism in Ukraine's military even as he acknowledged a difficult fight ahead