TAIPEI (Reuters) - Collaboration between the United States and Taiwan is stronger and more expansive than ever before, former chairman of the U.S. Joint Chiefs of Staff Mike Mullen said during his visit to the democratic island on Wednesday.

       Mullen is in Taiwan leading a delegation of former top officials sent by U.S. President Joe Biden. The trip is happening against the backdrop of Russia's invasion of Ukraine.

       (Reporting by Yimou Lee and Sarah Wu; Editing by Christopher Cushing)