South Korea's new ambassador to Australia said Thursday he will cooperate with anti-corruption investigators after being accused of interfering with a probe into a marine's death when he was defence minister last year.

The marine was swept away while doing relief work during major floods in July last year, and Seoul's Corruption Investigation Office (CIO) is looking into whether Lee Jong-sup, who was defence minister at the time, interfered with a probe of the accident.

Lee was under a travel ban due to the CIO inquiry, but was appointed ambassador to Canberra by President Yoon Suk Yeol and left to take up his post on 10 March.

He arrived back in Seoul Thursday, telling reporters he had returned to attend defence meetings but hoped to speak to the CIO while he was back. He has denied any wrongdoing.

"I hope to arrange schedule with the CIO so that I can undergo questioning during my stay", he told reporters at the airport.

Lawmakers from both the opposition and the ruling party have criticised the decision to allow Lee to leave the country for his new post while he was under investigation.

"He must resign and be questioned as a civilian" to avoid negative publicity for the Yoon government, said MP Kim Tae-ho of the ruling party in a Facebook post.

The ex-defence chief's posting to Australia was seen as an attempt by Seoul to help deepen defence cooperation with Canberra, which signed a $2.4 billion deal in December with South Korea's Hanwha Aerospace to purchase infantry fighting vehicles.

But appointing Lee as ambassador while he remains under investigation "defies common sense", conservative daily Chosun Ilbo said in a Wednesday editorial