TOKYO, Oct 3 (Reuters) - Japan's Nikkei share average slumped to a four-month low on Tuesday as sentiment soured amid higher U.S. yields and the Federal Reserve's pledge of an extended period of tight financial conditions.

The Nikkei lost 1.23% to 31,367.578 as of 0225 GMT, and earlier dipped as low as 31,260.99 for the first time since June 2.

Of the index's 225 components, 204 fell, with 20 gaining and one flat.

The broader Topix slipped about 1%.

The benchmark 10-year Treasury yield marched to a fresh 16-year peak above 4.7% overnight after Fed Governor Michelle Bowman and Fed Vice Chair for Supervision Michael Barr reiterated the higher rates for longer refrain at separate events.

The rise in long-term U.S. yields helped push the yen to the lowest in a year at close to 150 per dollar, but that failed to help lift Japanese exporter shares.

Toyota Motor sagged 2.1% and Mazda sank 4.5%.

"Normally yen weakness would be a reason for stocks to rise, particularly the exporters, because it boosts overseas profits," said Nomura Securities strategist Maki Sawada.

"But because the background for the move is a rise in long-term yields, it's a weight on the Nikkei."

Japanese government bond yields also pushed to new highs, with the 10-year yield reaching a 10-year peak of 0.78%.

The promise of extended tight financial conditions also weighed on crude oil, which tumbled 2% overnight.

As a result, energy shares were the biggest drag, slumping 5.14%.

Oil company Inpex was the worst-performing Nikkei stock, sagging 6.22%. JGC Holdings, an engineering company also involved in the oil business, was next with a 5.15% slide.

Tech stocks provided some relief, helped partly by the Nasdaq's outperformance overnight on Wall Street.

Online services providers LY Corp rose 1.21% to lead advancers, while Recruit Holdings added 0.81%. (Reporting by Kevin Buckland; Editing by Sohini Goswami)