TOKYO, June 29 (Reuters) - Japanese government bonds edged down in thin activity on Thursday, as investors waited for the Bank of Japan to reveal details of its regular bond-purchasing operations for July.

The central bank will disclose the details of its buying intentions in each zone for next month on Friday. The BOJ kept its ranges intact in June, after trimming the amount of shorter-dated JGBs it bought compared with previous months in May and April.

The 10-year cash JGB yield was untraded, while the September 10-year JGB futures contract finished down 0.08 point at 150.44.

Superlong yields were flat, while the yield on the two-year JGB edged up half a basis point to minus 0.120 percent.

The Ministry of Finance floated a plan on Wednesday to increase the size of short-term Japanese government bond issue through so-called liquidity-enhancing auctions to ease their shortage, a senior ministry official said.

The plan was proposed to a gathering of JGB primary dealers, the official said, adding the ministry will make a final decision on the plan after sounding out investors' opinions.

Economic data released earlier on Thursday showed Japanese retail sales rose less than expected last month, falling substantially from April's annual increase though analysts expect sales to continue rising as a trend. (Reporting by Tokyo markets team; Editing by Amrutha Gayathri)