President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE touted his good relations with Japan on Thursday but warned the relationship may sour over trade.

“Of course that will end as soon as I tell them how much they have to pay,” the president said of his strong ties with Japan in a call to Wall Street Journal assistant editor James Freeman.

Freeman shared the president's remarks in a WSJ op-ed published Thursday. Freeman said Trump had called him shortly after the editor appeared in a segment on the Fox News Channel praising the president for the strong U.S. economy.

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Trump's comments about Japan come as the U.S. finds itself in a number of trade fights with allies and other countries.

Trump has slapped tariffs on imported steel and aluminum. And he has threatened new tariffs on auto imports. Japan's trade minister in August warned the country could possibly retaliate.

Trump last week announced a trade deal with Mexico to replace the North American Free Trade Agreement. The U.S. is separately negotiating with Canada but both countries have dug in during the contentious talks.

Trump has warned he is willing to go ahead and sign the deal with Mexico if Canada does not get on board.

“[T]here is no political necessity to keep Canada in the new NAFTA deal,” Trump tweeted last week.

Canadian Prime Minister Trudeau has vowed his country is “not going to accept is that we should have to sign a bad deal just because the president wants it.”

Trump is also escalating a trade war with China. Trump has floated another $200 billion in tariffs on Chinese goods.