Japan's core consumer inflation hit a fresh 41-year high in January as companies passed on higher costs to households, data showed on Friday, keeping the central bank under pressure to phase out its massive stimulus program.

The data underscores the dilemma policymakers face as soaring prices of fuel and daily necessities hit households, many of whom have yet to see wages rise enough to make up for the higher cost of living.

The nationwide core consumer price index, which excludes volatile fresh food but includes energy costs, was 4.2 percent higher in January than a year earlier. January's rise was the fastest since September 1981, when fuel costs spiked due to a Middle East oil crisis that hit Japan's import-reliant economy.

The data showed that core consumer inflation has now exceeded the Bank of Japan's (BOJ) 2-percent target for nine straight months, mostly reflecting persistent rises in fuel and raw material costs.

"Inflation will probably peak in January but may not fall back below the BOJ's 2-percent target for some time," said Yoshimasa Maruyama, chief economist at SMBC Nikko Securities.

"But there are questions as to whether the rise in inflation will be sustainable, as it is still driven largely by food and fuel costs," he said.

Incoming Governor Kazuo Ueda faces a challenge in sustaining the BOJ's yield control policy, which has come under attack by markets betting strong inflation will force the bank to raise interest rates.

However, Ueda said on Friday the central bank must maintain ultra-low interest rates to support the fragile economy, warning of the dangers of responding to cost-driven inflation with monetary tightening.

"Japan's trend inflation is likely to rise gradually. But it will take some time for inflation to sustainably and stably achieve the BOJ's 2-percent target," he said.

"It's true there are various side-effects emerging from the stimulus. But the BOJ's current policy is a necessary, appropriate means to achieve 2-percent inflation."

(With input from Reuters)