The Corruption Investigation Office for High-ranking Officials(CIO) said additional questioning of Ambassador to Australia Lee Jong-sup would be necessary in its investigation into his alleged meddling of a case on the death of a Marine during a rain search operation last year.

At a press briefing on Tuesday, a CIO official said the position of the probe team stands that questioning should be conducted in person through summons by principle.

As for a questioning last week of Lee prior to taking the new ambassadorship, the official said the former defense minister had submitted a brief written testimony and a mobile phone.

Asked about difficulties in carrying out a face-to-face questioning of a suspect serving as an ambassador, the official said Lee had expressed a will to cooperate in the probe and that it is common for diplomats to return to their home country for public duties.

The official also displayed a sign of discomfort regarding the justice ministry's move to lift a travel ban imposed on Lee amid the ongoing investigation.