Prime Minister Shinzo Abe on Wednesday stood by embattled economy minister Akira Amari, but said Amari has a duty to separate fact from fiction in allegations he received cash for favors from a construction firm.

"I would like him to continue to tackle a range of important duties pertaining to economic revitalization and the Trans-Pacific Partnership agreement," Abe said during a plenary session of the Upper House.

"I'm confident that he will swiftly investigate the facts and fulfill his responsibility to explain himself."