By Steve Holland and Trevor Hunnicutt EVIAN-LES-BAINS, France, June 17 (Reuters) - U.S. President Donald Trump on Wednesday described Chinese President Xi Jinping and Russian President Vladimir Putin as "neutral" during the war with Iran, saying they had notthwarted his efforts to curbTehran's nuclear ambitions. "I just want to thank them because they made it a lot better," Trump said following the adoption of a ceasefire agreement in the conflict.