South Korea's business sentiment improved in April due to strong seasonality and eased concerns over external uncertainties, the central bank said Monday.

The monthly business survey index (BSI), which gauges local manufacturers' assessment of current business conditions, rose 3 points to 84 in April, but the seasonally-adjusted figure retreated 2 points to 80, according to the Bank of Korea (BOK).

The April gain in nominal reading was attributed to strong seasonality during the Spring season and reduced worries about external uncertainties such as Europe's debt crisis and high oil prices. "Entrepreneurs' sentiment over business conditions is generally boosted during the Spring season due to seasonality. Positive economic signs may boost the sentiment," an official at the BOK told Xinhua.

The official, however, noted that the April figure can be viewed as mixed because the seasonally-adjusted number declined, saying that it remained to be seen whether the next month's figure continue to be rise.

The BSI for May, measuring manufacturers' outlook on business conditions for the upcoming month, jumped 5 points on-month to 90, but the reading adjusted with seasonal factors stayed unchanged at 84, according to the BOK.

Local manufacturers picked weak domestic demand, high raw material prices and uncertain economic conditions as their difficulties in doing business.

Meanwhile, the monthly index for non-manufacturers gained 2 points on-month to 82 in April and the index for May advanced 3 points to 85. Local non-manufacturers regarded fragile domestic demand, fierce competition and economic uncertainties as their hardship.

The BSI index is based on a nationwide survey of 1,617 manufacturers and 888 non-manufacturers, conducted between April 16 and 23.