Japan will impose a 15 percent tariff on US steel starting Sep 1 in retaliation for duties imposed on Japanese products, a trade ministry official said Monday.

The higher tariffs are worth 5.7 billion yen ($51 million), according to Japan's finance ministry.

Japan requested the US repeal duties on Japanese steel products under the so-called Byrd amendment passed in 2000, an anti-dumping law ruled illegal by the World Trade Organisation (WTO).

The WTO ruled in January 2003 that the US measure unlawfully protected the American steel industry.

When it was not repealed by the end of that year, Japan, the European Union and six other countries won the right to impose a total of $150 million in economic sanctions against the US.