MEXICO CITY, Dec 16 (Reuters) - Mexico’s central bank on Wednesday said it had extended its $60 billion swap line with the U.S. Federal Reserve until September 2021. The Federal Reserve will keep open dollar “swap” lines, opened in March to help battle the economic fallout from the pandemic, for nine mid-sized foreign central banks until Sept. 30, 2021. (Reporting by Miguel Gutierrez; Writing by Drazen Jorgic)