SINGAPORE/BRUSSELS -- Japanese trade minister Hiroshige Seko on Saturday voiced strong concerns about the U.S. plan to raise tariffs on steel and aluminum imports during a phone conversation with U.S. Commerce Secretary Wilbur Ross, according to Japanese government sources.

The minister told Ross that steel and aluminum exports from Japan, a U.S. ally, do not affect U.S. national security, the sources said. Seko also said Japanese steel products are essential for both Japanese and U.S. companies and told Ross that they affect American employment as well, the sources added.

Seko was speaking from Singapore, where he was attending talks regarding the Regional Comprehensive Economic Partnership, a trade pact that is under negotiation.

The sources did not say how Ross reacted to Seko's remarks.

An official of the Japanese Ministry of Economy, Trade and Industry said the restrictions on steel and aluminum imports, unveiled by President Donald Trump on Thursday, will likely violate World Trade Organization rules.

The WTO allows members to limit trade on national security grounds. But the Japanese ministry official said the U.S.'s announcement "cannot be interpreted as such."

Japan, however, is expected to tread carefully as to whether to file a WTO complaint as it needs American cooperation in national security matters, such as those related to North Korea. Japan could, however, join the EU and other relevant members in filing a WTO complaint.

The EU is expected to counter the import restrictions, if Trump goes through with them, with about 2.8 billion euros ($3.4 billion) worth of retaliatory measures on U.S. exporters.

The European Commission, the executive arm of the EU, plans to propose tariffs of around 25% on American steel, other industrial goods and agricultural imports.

Meanwhile, Chinese Foreign Minister Wang Yi on Saturday criticized the U.S. move, calling it "baseless" and "unreasonable." He mentioned that a number of European countries as well as Canada have called it "unacceptable."

"It will not benefit the U.S., either," Wang added.