Annual core consumer inflation in Japan rose in September, but it remains half the central bank's 2 percent target, as the escalation of trade friction darkens economic prospects.

While the growth rates were the fastest in the last seven months, the increase was mainly due to an increase in oil spending, since the prices of most other commodities rose slightly, according to government data.

The National Consumer Price Index (CPI), which eliminates the impact of volatile spending on fresh food, rose 1.0% in September, after rising 0.9% in August.

The so-called core consumer price index, a more closely observed indicator used by the Bank of Japan, which excludes food prices and energy costs, was 0.4% in September.

Governor of the Bank of Japan, Haruhiko Kuroda, on Thursday offered a slightly more optimistic view on prices than three months ago, saying that the main consumer inflation "is moving towards 1%."

Rising energy prices may give the Bank of Japan a reason to slightly reconsider its inflation forecasts, although the increase may be mitigated by uncertainty about the consequences of trade friction, analysts say.

According to current forecasts made in July, the Bank of Japan expects core consumer inflation to reach 1.1% in the current fiscal year, which will end in March 2019, and accelerate to 1.5% next year.

The Japanese economy recovered in the second quarter after a decline in the first three months of this year, helped by sustainable business spending.

But the worsening trade frictions and a number of natural disasters that disrupted the supply chain overshadow the prospects for an export-dependent economy, with some analysts predicting a slight contraction in the third quarter.