By Junko Fujita

TOKYO, Sept 22 (Reuters) - Yields on Japan's nine-year bonds hovered close to 0.3% in early trade on Thursday as investors tested the Bank of Japan's resolve to pin down interest rates, following the U.S. Federal Reserve's aggressive policy tightening.

The BOJ is expected to keep interest rates ultra-low and reassure markets it will continue to swim against a global tide of central banks tightening monetary policy to combat soaring inflation.

But investors are challenging the move, sending yields on Japan's government bonds maturing in September 2031 as high as 0.286% in early trade, according to Tradeweb Markets, and last at 0.285%.

That's above the 0.25% upper limit the BOJ sets for benchmark 10-year yields, suggesting pressure is building in the market.

Ten-year bonds have not been priced yet, staying at the central bank's policy 0.25% limit, having been untraded for two-straight sessions as the BOJ continues to defend its yield target.

Japan has this week driven home its commitment to ultra-dovish policy by spending more than 2 trillion yen ($13.8 billion) in the past two days to hold a 0.25% ceiling on the 10-year Japanese government bond yield.

Overnight, the Fed hiked rates by 75 basis points and signaled more increases to come. Fed Chairman Jerome Powell said U.S. central bank officials are "strongly resolved" to bringing down inflation from the highest levels in four decades and "will keep at it until the job is done."

Japan's five-year yield fell 0.5 of a basis point to 0.060%, while other notes have not been priced as of 0115 GMT.

Benchmark 10-year JGB futures rose 0.05 of a point to 148.31, with a trading volume of 4,661 lots. (Reporting by Junko Fujita and the Tokyo markets team; Editing by Sam Holmes)