(Reuters) - U.S. President Donald Trump said on Sunday he will introduce 25% tariffs on all steel and aluminum imports into the United States, on top of existing metals duties, in another major escalation of his trade policy overhaul.

Here's a summary of the major trade partners it will affect.

Steel

Roughly a quarter of all steel used in the United States is imported, the bulk of it from neighbours Mexico and Canada or close allies in Asia and Europe like Japan, South Korea and Germany.

While China is the world's largest steel producer and exporter, very little is sent to the United States. Tariffs of 25% imposed in 2018 shut most Chinese steel out of the market.

China exported 508,000 net tons of steel to the U.S. last year or 1.8% of total American steel imports.

Aluminum

In the case of aluminum, the U.S. is more heavily reliant on imports. Roughly half all aluminum used in the U.S. is imported, The vast majority comes from neighbour Canada. At 3.2 million tons last year, Canadian imports were twice the next nine countries combined.

The next largest sources of imports are the United Arab Emirates and China at 347,034 and 222,872 metric tons, respectively.

The U.S. aluminum smelting industry is small by global standards. Total smelter capacity in the country was just 1.73% of the global total according to the U.S. geological survey.