* Ministry says performs more inspections over improper checks
* Nissan recalls 1.2 mln vehicles sold in Japan for re-inspections (Adds details, background on inspection issue)
TOKYO, Oct 4 (Reuters) - Japan's Transport Ministry said on Wednesday it had conducted raids at two plants producing Nissan Motor Co cars, in addition to four checks performed last week 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 matter told Reuters the recent raids showed that the names of certified technicians were used on inspection papers to sign off on final vehicle checks conducted by non-certified technicians.
It was possible that this had occurred at most or all of the six plants, they added. The sources declined to be identified as they were not authorised to speak to the media.
Nissan confirmed the ministry had conducted on-site inspections at its Tochigi and Kyoto Autoworks plants.
"We are currently conducting an investigation (with third-party assistance) into the nature of this vehicle inspection issue at our plants," spokesman Nick Maxfield said in an emailed statement.
Nissan's recall is the second major misconduct incident involving a Japanese automaker in as many years, after Mitsubishi Motors Corp admitted in April 2016 it had falsified the fuel economy of some of its domestic market models.
The recall includes all of the 386,000 passenger vehicles Nissan sold in Japan in 2016, roughly 10 percent of its global sales, and comes at a time when Nissan has been enjoying strong domestic sales of its Serena minivan and Note compact hatchback.
(Reporting by Maki Shiraki and Naomi Tajitsu; Editing by Edwina Gibbs)