Japan's core consumer price index in December rose at a slower pace than expected, the government said Friday, adding to doubts that the Bank of Japan will raise interest rates next month.

The core CPI, which excludes volatile fresh food prices but includes energy prices, rose 0.1 percent in December from a year before, the Ministry of Internal Affairs and Communications said. The figure is below a 0.2 percent increase that economists on average had forecast.

The reading came after the core CPI in November rose 0.2 percent on year. Japan's inflation slowed mainly due to a recent decline in crude oil prices, a cut in mobile phone charges and prolonged discounting of airline tickets, according to a government official.