President Donald Trump tweeted Wednesday that the U.S. is not in a trade war with China – and "that war was lost many years ago" by previous U.S. leadership.

"We are not in a trade war with China, that war was lost many years ago by the foolish, or incompetent, people who represented the U.S.," Trump said.

@realDonaldTrump: We are not in a trade war with China, that war was lost many years ago by the foolish, or incompetent, people who represented the U.S. Now we have a Trade Deficit of $500 Billion a year, with Intellectual Property Theft of another $300 Billion. We cannot let this continue!

Trump said the U.S. cannot let its trade deficit with China continue. The tweet came hours after China unveiled plans for new tariffs on 106 U.S. products. Stock futures sank, with the Dow Jones industrial average set for a 500-point decline.

The president doubled-down on his view of the trade deficit in a later tweet, saying the current situation means the U.S. "can't lose."

@realDonaldTrump: When you're already $500 Billion DOWN, you can't lose!

The effective start date for China's new tariffs will be revealed later, although China's Ministry of Commerce said the charges are designed to target up to $50 billion in U.S. products annually. The 25 percent levy on U.S. imports includes products such as soybeans, cars and whiskey, Beijing said.

China's ambassador to the United States explained to CNBC on Tuesday evening why his country was striking back against U.S. trade measures.

"We certainly don't want to have any trade war with anybody, but people have to understand who started all this," Ambassador Cui Tiankai said.

Speaking ahead of the official announcement, Tiankai said China would resort to the World Trade Organization dispute settlement mechanism.

Cui's comments come after Trump's White House on Tuesday unveiled a list Chinese imports the administration proposes to target as part of a crackdown on what the president deems unfair trade practices.

In an interview with CNBC on Wednesday morning, Commerce Secretary Wilbur Ross, who is one of the main players in Trump's trade strategy, said China's new tariffs aren't a threat to the U.S.