By Kevin Buckland

TOKYO The Bank of Japan announced an unscheduled bond operation on Tuesday, as it sought to slow a rise in Japanese government bond (JGB) yields that had brought them to fresh decade highs.

Japan's central bank offered to buy 300 billion yen ($2.00 billion) in bonds with maturities of five to 10 years and 100 billion yen worth with maturities of 10-25 years from Wednesday.

That was in addition to its daily offer to buy an unlimited amount of JGBs at a fixed rate of 1%.

Following the BOJ's announcement, the 10-year JGB yield declined 0.5 basis point to 0.855%, earlier trading unchanged from Monday's closing level of 0.86%, which was the highest since July 2013.

Japanese yields have been pulled higher by a surge in U.S. Treasury yields, with the benchmark 10-year note topping 5% overnight to reach a 16-year high. [US/]

The BOJ caps the 10-year yield at 1% under its yield curve controls (YCC), following a surprise policy tweak at the end of July. Although the yield remains well below that level, policymakers have stepped in repeatedly to slow the pace of increases.

The central bank next sets policy on Oct. 31.

($1 = 149.6500 yen)

(Reporting by Kevin Buckland; Editing by Christopher Cushing and Jacqueline Wong)