TOKYO, Oct 4 (Reuters) - Japan's Transport Ministry said on Wednesday it had conducted raids at two plants producing Nissan Motor Co cars as part of a probe into unauthorised vehicle inspections.

Nissan said this week it would recall all 1.2 million new passenger cars it sold in Japan over the past three years after discovering final vehicle inspections were not performed by authorised technicians at six factories.

Two sources with knowledge of the the matter told Reuters the names of certified technicians were used on inspection papers to sign off on final vehicle checks conducted by non-certified technicians.

The sources declined to be identified as they were not authorised to speak to the media. Nissan declined immediate comment.

(Reporting by Maki Shiraki and Naomi Tajitsu; Editing by Edwina Gibbs)