SEOUL, South Korea — South Korea's central bank Thursday cut its forecasts for economic growth this year, citing a weaker-than-expected fourth quarter.

Bank of Korea Governor Lee Ju-yeol said Asia's fourth-largest economy will expand 3.4 percent in 2015, not 3.9 percent the central bank predicted in October.

The bank also lowered its inflation forecast. It expects consumer prices to rise 1.9 percent this year, instead of 2.4 percent, because of lower crude oil prices.

Lee said that the fourth quarter of last year was unexpectedly weak due to "unusual elements" such as lower government spending and a drop in mobile device sales due to new regulations.

The bank estimated that South Korean economy likely expanded 0.4 percent in the fourth quarter from the previous quarter, less than the 1 percent forecast.

Lee said businesses need to boost investment in order to increase household income, which in turn, leads to a boost in consumption.

The Bank of Korea left its benchmark interest rate unchanged at a record low level of 2 percent. The top central banker said the current level is sufficiently low to provide support to economic recovery.