The concentration of impurity in steel a Japanese manufacturer supplied to nuclear facilities in France exceeded the standards set by the European country, Japan’s nuclear watchdog said Wednesday, meaning the steel could be weaker than expected.

Briefed recently by French regulators about the finding, the Nuclear Regulation Authority is looking into allegations regarding the products provided by the Kitakyushu-based firm under scrutiny, Japan Casting & Forging Corp.

The NRA said it needs to carry out tests to evaluate whether the steel is in fact lacking in strength.

The French regulators said in June they found steel containing larger-than-expected amounts of impure substances in facilities such as reactor pressure vessels at 18 reactors operating in France and are investigating the matter. The steel products in question were made by Japan Casting & Forging and Creusot Forge, a subsidiary of France’s Areva SA.

In August, the NRA ordered local utilities hosting nuclear power plants in Japan to examine reactors and other major parts at the plants. The utilities have been asked to report the results to the NRA by the end of October.

Japan Casting & Forging is also under scrutiny in Japan as it is responsible for the construction of reactor pressure vessels in 13 Japanese nuclear reactors including the Sendai Nos. 1 and 2 reactors operated by Kyushu Electric Power Co. in Kagoshima Prefecture.

Currently, the two Sendai reactors are operating in Japan after passing stricter safety checks in the wake of the 2011 nuclear crisis that crippled the Fukushima No. 1 nuclear power plant in Fukushima Prefecture.

Japan Casting & Forging had said earlier it has removed the impurities from its steel as instructed by its clients.

The NRA said the standard for carbon content in metals — a gauge of impurity — is below 0.22 percent in France, while the figure in Japan is below 0.25 percent.

But in some products provided by the Japanese firm in some nuclear facilities, carbon content in steel was over 0.3 percent.