TOKYO, June 23 (Reuters) - Japan's Nikkei share average

fell on Monday as U.S. attacks on Iranian nuclear sites fueled

risk aversion, while the accompanying jump in oil prices weighed

on the outlook for Japan's economy and corporate earnings.

The Nikkei sank 0.55% to 38,191.87 as of the midday

recess, with 161 of its components declining, versus 60 that

rose and four that traded flat.

The broader Topix slumped 0.62%.

Japan imports almost all of its oil, making the economy

highly sensitive to crude prices, which surged to six-month

peaks on Monday as traders waited nervously to see Iran's

response to the U.S.'s entry into the conflict. Japanese

manufacturers are also vulnerable to energy price spikes.

At the same time, analysts pointed to the yen's decline to a

nearly six-week low versus a broadly stronger U.S. dollar as

providing some support to shares in Japan's heavyweight

exporters, whose overseas revenues gain in value when the yen

weakens.

"The rise in the dollar-yen interest rate has been very

clearly helpful for the Nikkei's performance," said Yunosuke

Ikeda, chief macro strategist at Nomura Securities.

The safe-haven yen is weakening because "investors seem more

focused this time on the impact of higher oil prices on Japan's

trade balance," Ikeda said.

Chip-sector stocks underperformed, with Screen Holdings ( DINRF )

falling 3.76% to be the Nikkei's biggest decliner in

percentage terms, while Tokyo Electron ( TOELF ) and Advantest ( ADTTF )

were the biggest drags in index-point terms with

respective declines of 2.42% and 1.69%.

The best performing stocks were oil explorers and refiners,

with the Topix mining sub-index climbing 1.49% and

the oil and coal sub-index adding 0.51%.

(Reporting by Kevin Buckland; Editing by Mrigank Dhaniwala)