Former defense chief and Ambassador to Australia Lee Jong-sup, who is a key suspect in a probe into alleged interference in the case of death of a Marine last year, urged the anti-corruption agency to accelerate its investigation.

Lee's lawyer Kim Jae-hoon said on Wednesday that his client has submitted a written opinion to the Corruption Investigation Office for High-ranking Officials(CIO), calling for the agency to swiftly investigate and come to a decision.

Lee claimed that the CIO has yet to contact him since he resigned from his ambassadorship amid controversy caused by the probe, adding such neglect has led to the opposition calling for a special counsel investigation.

The former defense chief said the opposition-sought special counsel probe into the death of late Cpl. Chae Su-geun during a search and rescue operation last year could set a bad precedent by adversely affecting an ongoing trial.

Lee also reiterated his denial of any legal violations in the handling of the initial Marine death investigation, saying the opposition's allegations of interference are a part of its political offensive.