The Bank of Japan left its assessment of the nation's economy unchanged for the fourth straight month Thursday, blaming lackluster economic activity and growing tensions surrounding Iraq and North Korea.

"Economic activity remains flat amid substantial uncertainty about the outlook for the economy," the central bank said in its monthly report of economic and financial developments.

The economy is unlikely to show any clear sign of recovery for some time because production is expected to remain unchanged amid persistent downward pressure, including excessive labor input and debt, it said.

Japan must keep a close watch on downside risks to the economy from overseas economies, it said, apparently alluding to the crises centering on Iraq and North Korea.

On the domestic front, Japan must carefully monitor progress by financial institutions to dispose of their nonperforming loans, it said.