(Updates with market reaction to JGB auction)

TOKYO, June 12 (Reuters) -

Long-dated Japanese government bond yields rose briefly on

Thursday, reversing earlier declines, following weak demand at a

government auction of the debt.

The Ministry of Finance received bids worth 897.8

billion yen ($6.24 billion) and sold 449.8 billion yen of debt

in a so-called liquidity enhancement auction for JGBs with

15.5-39 years left to maturity.

The demand was much lower than the previous sale in

April, when the finance ministry received 1.555 trillion yen in

bids and sold 649.3 billion yen of bonds.

The 20-year JGB yield advanced 1.5 basis

points (bps) to 2.395% immediately following the announcement of

the auction results, before falling again to be down 0.5 bp as

of 0423 GMT.

The 30-year yield briefly flipped to a 0.5 bp

rise but was last 1 bp lower at 2.905%.

"The liquidity supply auction yielded a distinctly

lackluster result, underscoring the market's subdued appetite

for super-long positions," said Shoki Omori, chief desk

strategist at Mizuho Securities.

"Although this outcome was generally within the expected

range, it nevertheless highlighted the lingering vulnerability

and volatility in the super-long segment."

Yields on 30-year JGBs surged to record highs last

month, and 20-year yields spiked to quarter-century peaks, as

investors turned skittish on the fiscal outlook for Japan and

other developed economies. The rise was exacerbated by reduced

appetite for the debt from life insurers and other traditional

domestic buyers.

The finance ministry injected some calm into the market

with a

pledge

to adjust the size of super-long JGB issuances, but there

are no details on how much the government will pare that back

and which shorter-dated tenors will see increased issuance as a

result.

JGB yields began the day by falling, tracking overnight

moves in U.S. Treasury yields.

The 10-year JGB yield fell 1 bp to 1.445%.

The five-year yield was down 1 bp at 1.005%,

and the two-year yield was flat at 0.75%.

($1 = 143.9300 yen)