TOKYO, April 9 (Reuters) - Japanese government bonds

slipped on Thursday, as growing uncertainty over a fragile

two-week ceasefire between the United States and Iran weighed on

investor sentiment.

The 10-year JGB yield rose 2.5 basis points

(bps) to 2.39%. Yields move inversely to bond prices.

"Optimism over the outlook of the Middle East war faded,

with doubts about the reopening of the Strait of Hormuz," said

Naoya Hasegawa, chief bond strategist at Okasan Securities.

Investor sentiment dampened after Israel launched its

heaviest strikes yet on Lebanon on Wednesday, killing hundreds

of people and prompting threats of retaliation from Iran. Tehran

also signalled that it would be "unreasonable" to continue

negotiations on a permanent peace deal with the United States.

The five-year yield rose 1.5 bps to 1.800%,

trimming the earlier climb of 2 bps following an auction, which

was labelled as 'relatively firm' by the market.

"The yield was an attractive level, and investors wanted to

buy the newly issued bonds for their portfolio," said Katsutoshi

Inadome, senior strategist at Sumitomo Mitsui Trust Asset

Management.

The finance ministry sold about 250 billion yen ($1.57

billion) of No. 184 five-year bonds, compared with the current

benchmark issue, No. 183.

The auction followed a disappointing 10-year bond sale last

week, which triggered a sell-off of JGBs and sent the 10-year

bond yield to a 27-year high on Tuesday.

Super-long bonds also trimmed gains in the afternoon

session. The 20-year JGB yield rose 2 bps to

3.285%, and the 30-year yield inched up 0.5 bp to

3.6%, after rising to 3.655%.

The two-year yield rose 1 bp to 1.385%.

($1 = 158.7500 yen)