KIEV, Nov. 15 - Ukrainian investigators said they had opened a criminal case into suspected extortion by officials at a sister anti-corruption agency, based partly on information from a whistleblower who also implicated the president’s office, Reuters reported.

The National Agency on Corruption Prevention (NAZK) is a keystone of Western-backed reforms but has been criticized for making slow progress with its main task of verifying officials’ wealth declarations for evidence of ill-gotten gains.