TOKYO -- Bank of Japan (BOJ) Governor Toshihiko Fukui has brushed aside political pressure to buy sagging bank shares to boost the share market after it sank to a 20 year low earlier this week.

In an interview with invited media released Friday, Fukui said the Central Bank's activity in the markets had to be strictly controlled.

"The primary job of the Central Bank is in the background, and our duty is to help provide a comfortable environment for private sector companies and banks to operate," Fukui said.

"If we do more, it clearly goes too far beyond the jurisdiction of the Central Bank," he added.

"The Central Bank cannot take limitless risk, which is rather the job that only the government can do," he said.

Japan's ruling coalition is reportedly planning to ask the BOJ to buy bank shares as part of emergency economic proposals aimed at halting the prolonged slide in stock prices, AFP reported.

The Central Bank has already been buying shares held by banks to reduce the exposure of lenders to the stock market slump. The maximum amount the bank will buy was lifted last month to three trillion yen ($25 billion) from two trillion yen.

The BOJ said its purchases of shares held by banks had so far totaled 1.25 trillion yen.

But Fukui said the existing measures were different from the new proposals and were narrowly aimed at protecting banks from share price fluctuations. "Buying bank shares directly is clearly different from purchasing non-bank shares from banks."

He warned that acting to counter short term factors including falling stock prices and the fallout from the outbreak of severe acute respiratory syndrome (SARS) following the end of the war in Iraq would distort economic policy.

"If we become hostage to short-term developments, we may lose the long term viewpoint and may mismanage the policy," he said.