Wholesale prices rose 4.1 percent in April from a year earlier for the 13th straight monthly increase, boosted by the effects of the April 1 consumption tax hike, the Bank of Japan said Wednesday.

The index of corporate goods prices stood at 105.7 against the 2010 base of 100, the BOJ said in a preliminary report. Excluding the impact of the tax hike, prices rose 1.4 percent from a year earlier, compared with a 1.7 percent increase in March.

"Corporate prices were strongly influenced by the effects of the consumption tax hike," a BOJ official said.

Excluding the impact of the consumption tax hike, however, the year-on-year price gain narrowed due to the diminishing effects of the weakening yen and rising energy prices, the official said.

"As seen in prices of chemical and other products, market prices have been falling because of the Chinese economy's uncertain prospects," the official added.

Prices of iron and steel expanded 7.3 percent in April from a year earlier amid increasing tensions that have hit Ukraine and concerns about economic sanctions against Russia, the official said.

Prices of electric power, gas and water surged 12.5 percent, reflecting the tax increase and rising electricity prices for industrial use.

Meanwhile, prices of chemical products fell excluding the impact of the tax hike due to falling medicine prices used in hospitals following a price revision, the official said.

On a month-on-month basis, the index rose 2.8 percent from March, also affected by the consumption tax hike increase.

Export prices in yen terms climbed 1.5 percent and import prices rose 2.6 percent, excluding the impact of the tax hike, due to the yen's depreciation against other major currencies.

On a contract currency basis, export prices fell 1.7 percent while import prices dropped 1.1 percent.