Japan slammed as "extremely regrettable" US President Donald Trump's sweeping new tariffs, saying they may break WTO rules and the two countries' trade agreement.

Japanese firms are the biggest investors in the United States but Tokyo has failed to secure an exemption, with Trump announcing a hefty 24-percent levy on Japanese imports.

"I have conveyed that the unilateral tariff measures taken by the United States are extremely regrettable, and I have again strongly urged [Washington] not to apply them to Japan," said Yoji Muto, trade and industry minister.

He said he spoke to US Commerce Secretary Howard Lutnick before Trump's announcement of a new 10-percent baseline tariff and extra levies on selected countries – including close strategic ally Japan.

"Japan [is] very very tough. Great people.... They would charge us 46 percent, and much higher for certain items," Trump said. "We are charging them 24 percent."

Muto said he had explained to Lutnick "how the US tariffs would adversely affect the US economy by undermining the capacity of Japanese companies to invest".

"We had a frank discussion on how to pursue cooperation in the interest of both Japan and the United States that does not rely on tariffs," Muto said.

Government spokesman Yoshimasa Hayashi also said the US measures may contravene World Trade Organization (WTO) rules and the two countries' trade treaty.

"We have serious concerns as to consistency with the WTO agreement and Japan-US trade agreement," he said.

Asked if Japan will impose retaliatory tariffs or is considering filing a suit to the WTO, Hayashi said: "We decline to disclose details of our considerations." (AFP)