KIEV, Oct. 20 - Moody's Investors Service has changed its outlook on Ukraine's key ratings to stable from positive as the global liquidity crunch has combined with existing macroeconomic, financial and political challenges.

"As a result, the probability that Moody's would raise the credit rating to Ba3 from B1 in the next 12 to 18 months has diminished, prompting the change in outlook," said Moody's Vice President Jonathan Schiffer.