Nuts are seen being prepared for shipment at the Mariani Nut Company in Winters, California, U.S. April 2, 2018. REUTERS/Elijah Nouvelage

GENEVA (Reuters) - China has notified the World Trade Organization it is imposing $611.5 million worth of retaliatory tariffs on $2.75 billion worth of U.S. imports including pork, nuts and ethanol in response to U.S. duties on aluminum and steel, a WTO document showed.

The document, dated last Thursday but posted only after the Easter public holidays, came after China said late on Sunday it has increased tariffs by up to 25 percent on 128 U.S. products, escalating a dispute between the world’s biggest economies.

China has fulfilled its legal duty to notify the WTO and other member states of its retaliatory measures.