File photo shows a liquefied natural gas tanker that traveled from Sakhalin 2 arriving off Sodegaura, Chiba Prefecture, in April 2009. (Kyodo)

TOKYO - Japan plans to retain its interest in the Sakhalin 2 oil and gas project and will notify Russia of its intention by the early September deadline, with two major Japanese energy companies set to sign on, sources familiar with the matter said Friday.