TOKYO, May 7 (Reuters) - Japanese government bond (JGB) yields were mixed on Tuesday as the Bank of Japan (BOJ) left bond purchase offers unchanged, shifting the focus to the central bank's summary of opinions due later this week.

While some market participants believed the BOJ could reduce purchase offers in the morning, the regularly scheduled bond purchase operation passed without incident, supporting bond buying.

The 10-year JGB yield fell 3 basis points (bps) to 0.870%, while the benchmark 10-year futures edged up 0.37 yen to 144.66 yen. Bond yields move inversely to prices.

Investors remain cautious, however, ahead of Thursday's release of a summary of opinions from the BOJ's April meeting, which could provide clues of its policy outlook and plans for reducing bond purchases.

The BOJ struck what markets took as a dovish stance at its April meeting, despite pressure from a yen languishing at 34-year lows.

It also maintained its guidance about buying government bonds, dashing hopes by some traders that it could soon taper purchases.

But hawkish whispers may have been missed, BOJ watchers say.

Investors may now be rethinking their initial assessment, said Naka Matsuzawa, chief macro strategist at Nomura Securities.

"It's quite obvious now that the BOJ is preparing its way to cut JGB purchases," he said, pointing to an analysis of the bank's bond purchases in the full text of its quarterly outlook report published after the April meeting.

"That was a very unusual outlook report that covered an analysis of JGB purchases, which is not usually in the report. It just came out from nowhere."

Investors were also eyeing an auction for 10-year bonds scheduled for Wednesday.

The two-year yield edged down 1 bp to 0.275% and the five-year yield slipped 1.5 bp at 0.470%.

The 20-year JGB yield had yet to trade as of 0520 GMT.

The 30-year JGB yield was flat at 1.980%. (Reporting by Brigid Riley; Editing by Varun H K)