TOKYO, Aug 18 (Reuters) - Japanese government bond prices were steady to a touch firmer on Friday with the market underpinned after gains by U.S. Treasuries and a regular debt-buying operation by the Bank of Japan.
A drop in Tokyo shares, with the Nikkei hitting a three-month low on weaker Wall Street and stronger yen, also supported JGBs.
The five-year yield dipped half a basis point to minus 0.090 percent. The benchmark 10-year yield and the 40-year yield were unchanged at 0.040 percent and 1.070 percent respectively.
The BOJ on Friday bought a total of 1.05 trillion yen ($9.60 billion) of one- to 10-year JGBs as part of its regular bond-purchasing operation.
U.S. Treasury prices rose on Thursday as investors, unnerved by a deadly attack in Barcelona and speculation about a top White House economic adviser quitting, favored safe and low-yielding bonds over stocks and other risky assets.
($1 = 109.4300 yen) (Reporting by the Tokyo markets team; Editing by Sherry Jacob-Phillips)