Six to seven banks spent about 7 million yen entertaining an executive of the Bank of Japan over the past five years, according to sources at the banks.

The central bank executive, who was not named, works in the credit and market management department, which is responsible for monitoring and executing operations for liquidity control in the money market, spawning allegations that he may have leaked information about the central bank's market operations in exchange for favors in the form of entertainment.

The Industrial Bank of Japan spent the most money -- some 3.3 million yen -- on about 90 occasions to entertain the central bank official, followed by Sanwa Bank, which spent about 1.5 million yen on several occasions, including seven golf tours, sources at the two banks said.

Sumitomo Bank, Sakura Bank, the Bank of Tokyo-Mitsubishi and Fuji Bank allegedly spent 500,000 yen to 1 million yen each on entertaining the central bank official, sources at these banks said.

Commercial banks are interested in the BOJ's moves to increase, decrease or maintain fund levels to control money market interest rates.

If any information is leaked beforehand, market players could gain privileged access to low-cost funds.

Tokyo prosecutors have been questioning commercial bank officials in charge of money market operations about what specific favors they offered to the BOJ official and what information they obtained, the sources said.