Japan's key inflation gauge slowed in September for the first time in five months, ahead of a central bank meeting later this month where the board is widely expected to keep the interest rate unchanged.

Consumer prices excluding fresh food rose 2.4% from a year earlier, decelerating from 2.8% in August as government utility subsidies softened the impact of ongoing inflation, according to the Internal Affairs Ministry on Friday. The result came in slightly stronger than the consensus estimate of 2.3%.

The slowdown in price gains largely hangs on government subsidies, thus it is likely to have a limited amount of impact on the Bank of Japan's (BOJ) policy path, provided there are no other signs of weakening in the trend. For Prime Minister Shigeru Ishiba, a waning of inflation may help his case as he heads into a general election on Oct 27.

Overall inflation slowed to 2.5% from 3% in August. Drops in electricity and gas prices drove the gauge lower, with the government's subsidies knocking 0.55 percentage points off.

A deeper index excluding energy costs and fresh food prices rose to 2.1% from 2% in the previous month. Service prices, seen by the BOJ as a key measure to examine the price trend, gained 1.3% from a year earlier, slowing from 1.4% in August.

BOJ is widely expected to leave the benchmark rate at 0.25% on October 31. The central bank's communication remains in focus after it was criticised for its last interest hike in July, which was followed by a global market crash shortly afterwards.

The bank has maintained its stance that it will reduce monetary easing further with additional rate hikes if inflation develops in line with its own projections. The BOJ's outlook will also be updated at the end of the month.

Japan's inflation has stayed at or above the BOJ's 2% target for two and half years. But so far Ishiba's government hasn't declared an exit from deflation, and has called for a cautious judgment on the pace of BOJ's interest rate hikes.