HONG KONG (MarketWatch) — Japan’s core consumer-price index fell in October, signaling the return of deflation after four months of price gains, and raising fresh doubts about the Bank of Japan’s claim of a trend change in the price environment.

Core CPI fell 0.1% in October, matching analyst forecasts compiled by Dow Jones Newswires. The CPI result followed a 0.2% rise in September.

Euro-zone running out of time

Much of the core CPI decline is related to an increase in cigarette taxes and insurance premiums that were unveiled in the same month a year earlier, analysts said.

Gas and electricity charges were higher from a year earlier, reflecting higher prices for liquid natural gas as conventional power stations were throttled up to compensate as nuclear power stations throttled back.

Societe Generale analysts said the CPI price drop would reignite concerns of a deepening price slump weighed by weaker global activity.

“The Bank of Japan has been assessing that the deflation in Japan is gradually easing. That may have been true until a few months ago, but there is an increasing sign that the trend has changed tack,” said Societe Generale’s Takuji Okubo in Tokyo, in a note following the CPI release.

He said the price environment would likely see the Bank of Japan broaden the scope of asset purchases beyond government bonds to include equity ETF purchases.

“The fresh evidence of decline in general prices suggests that the BOJ should also need to influence more general risky asset prices,” Okubo said.

Barclays Capital said it expects the core CPI to hover between negative 0.1% and positive 0.1% until March, and then fall off more steeply.