SEOUL, South Korea — A close political ally of President Moon Jae-in of South Korea conspired with a team of online bloggers to illegally influence public opinion ahead of Mr. Moon’s election last year, a special counsel said Monday.

The special counsel, Huh Ik-bum, whose investigation was authorized by the National Assembly, found no evidence that Mr. Moon himself was involved in the alleged scheme. Mr. Huh also did not determine whether or how much Mr. Moon profited politically from the online operation.

But the alleged involvement of Kim Kyoung-soo, one of Mr. Moon’s closest aides, is a political setback for Mr. Moon, who has vowed to set himself apart from South Korea’s former presidents and their ethical scandals. Almost all of South Korea’s presidents, including Mr. Moon’s immediate predecessor, Park Geun-hye, were entangled in corruption scandals that implicated them or their aides and relatives.

Mr. Kim was accused of working with an internet blogger named Kim Dong-won, known widely here by his blogging alias, Druking.